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Nontotient

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In number theory, a nontotient is a positive integer n which is not a totient number: it is not in the range of Euler's totient function φ, that is, the equation φ(x) = n has no solution x. In other words, n is a nontotient if there is no integer x that has exactly n coprimes below it. All odd numbers are nontotients, except 1, since it has the solutions x = 1 and x = 2. The first few even nontotients are this sequence:

14, 26, 34, 38, 50, 62, 68, 74, 76, 86, 90, 94, 98, 114, 118, 122, 124, 134, 142, 146, 152, 154, 158, 170, 174, 182, 186, 188, 194, 202, 206, 214, 218, 230, 234, 236, 242, 244, 246, 248, 254, 258, 266, 274, 278, 284, 286, 290, 298, ... (sequence A005277 in the OEIS)

The least value of k such that the totient of k is n are (0 if no such k exists) are this sequence:

1, 3, 0, 5, 0, 7, 0, 15, 0, 11, 0, 13, 0, 0, 0, 17, 0, 19, 0, 25, 0, 23, 0, 35, 0, 0, 0, 29, 0, 31, 0, 51, 0, 0, 0, 37, 0, 0, 0, 41, 0, 43, 0, 69, 0, 47, 0, 65, 0, 0, 0, 53, 0, 81, 0, 87, 0, 59, 0, 61, 0, 0, 0, 85, 0, 67, 0, 0, 0, 71, 0, 73, ... (sequence A049283 in the OEIS)

The greatest value of k such that the totient of k is n are (0 if no such k exists) are this sequence:

2, 6, 0, 12, 0, 18, 0, 30, 0, 22, 0, 42, 0, 0, 0, 60, 0, 54, 0, 66, 0, 46, 0, 90, 0, 0, 0, 58, 0, 62, 0, 120, 0, 0, 0, 126, 0, 0, 0, 150, 0, 98, 0, 138, 0, 94, 0, 210, 0, 0, 0, 106, 0, 162, 0, 174, 0, 118, 0, 198, 0, 0, 0, 240, 0, 134, 0, 0, 0, 142, 0, 270, ... (sequence A057635 in the OEIS)

The number of ks such that φ(k) = n are (start with n = 0) are this sequence:

0, 2, 3, 0, 4, 0, 4, 0, 5, 0, 2, 0, 6, 0, 0, 0, 6, 0, 4, 0, 5, 0, 2, 0, 10, 0, 0, 0, 2, 0, 2, 0, 7, 0, 0, 0, 8, 0, 0, 0, 9, 0, 4, 0, 3, 0, 2, 0, 11, 0, 0, 0, 2, 0, 2, 0, 3, 0, 2, 0, 9, 0, 0, 0, 8, 0, 2, 0, 0, 0, 2, 0, 17, ... (sequence A014197 in the OEIS)

Carmichael's conjecture is that there are no 1s in this sequence.

An even nontotient may be one more than a prime number, but never one less, since all numbers below a prime number are, by definition, coprime to it. To put it algebraically, for p prime: φ(p) = p − 1. Also, a pronic number n(n − 1) is certainly not a nontotient if n is prime since φ(p2) = p(p − 1).

If a natural number n is a totient, n · 2k is a totient for all natural numbers k.

There are infinitely many even nontotient numbers: indeed, there are infinitely many distinct primes p (such as 78557 and 271129, see Sierpinski number) such that all numbers of the form 2ap are nontotient, and every odd number has an even multiple which is a nontotient.

n numbers k such that φ(k) = n n numbers k such that φ(k) = n n numbers k such that φ(k) = n n numbers k such that φ(k) = n
1 1, 2 37 73 109
2 3, 4, 6 38 74 110 121, 242
3 39 75 111
4 5, 8, 10, 12 40 41, 55, 75, 82, 88, 100, 110, 132, 150 76 112 113, 145, 226, 232, 290, 348
5 41 77 113
6 7, 9, 14, 18 42 43, 49, 86, 98 78 79, 158 114
7 43 79 115
8 15, 16, 20, 24, 30 44 69, 92, 138 80 123, 164, 165, 176, 200, 220, 246, 264, 300, 330 116 177, 236, 354
9 45 81 117
10 11, 22 46 47, 94 82 83, 166 118
11 47 83 119
12 13, 21, 26, 28, 36, 42 48 65, 104, 105, 112, 130, 140, 144, 156, 168, 180, 210 84 129, 147, 172, 196, 258, 294 120 143, 155, 175, 183, 225, 231, 244, 248, 286, 308, 310, 350, 366, 372, 396, 450, 462
13 49 85 121
14 50 86 122
15 51 87 123
16 17, 32, 34, 40, 48, 60 52 53, 106 88 89, 115, 178, 184, 230, 276 124
17 53 89 125
18 19, 27, 38, 54 54 81, 162 90 126 127, 254
19 55 91 127
20 25, 33, 44, 50, 66 56 87, 116, 174 92 141, 188, 282 128 255, 256, 272, 320, 340, 384, 408, 480, 510
21 57 93 129
22 23, 46 58 59, 118 94 130 131, 262
23 59 95 131
24 35, 39, 45, 52, 56, 70, 72, 78, 84, 90 60 61, 77, 93, 99, 122, 124, 154, 186, 198 96 97, 119, 153, 194, 195, 208, 224, 238, 260, 280, 288, 306, 312, 336, 360, 390, 420 132 161, 201, 207, 268, 322, 402, 414
25 61 97 133
26 62 98 134
27 63 99 135
28 29, 58 64 85, 128, 136, 160, 170, 192, 204, 240 100 101, 125, 202, 250 136 137, 274
29 65 101 137
30 31, 62 66 67, 134 102 103, 206 138 139, 278
31 67 103 139
32 51, 64, 68, 80, 96, 102, 120 68 104 159, 212, 318 140 213, 284, 426
33 69 105 141
34 70 71, 142 106 107, 214 142
35 71 107 143
36 37, 57, 63, 74, 76, 108, 114, 126 72 73, 91, 95, 111, 117, 135, 146, 148, 152, 182, 190, 216, 222, 228, 234, 252, 270 108 109, 133, 171, 189, 218, 266, 324, 342, 378 144 185, 219, 273, 285, 292, 296, 304, 315, 364, 370, 380, 432, 438, 444, 456, 468, 504, 540, 546, 570, 630

References

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  • Guy, Richard K. (2004). Unsolved Problems in Number Theory. Problem Books in Mathematics. New York, NY: Springer-Verlag. p. 139. ISBN 0-387-20860-7. Zbl 1058.11001.
  • L. Havelock, A Few Observations on Totient and Cototient Valence from PlanetMath
  • Sándor, Jozsef; Crstici, Borislav (2004). Handbook of number theory II. Dordrecht: Kluwer Academic. p. 230. ISBN 1-4020-2546-7. Zbl 1079.11001.
  • Zhang, Mingzhi (1993). "On nontotients". Journal of Number Theory. 43 (2): 168–172. doi:10.1006/jnth.1993.1014. ISSN 0022-314X. Zbl 0772.11001.
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