A333633 Smallest m such that sigma(m) == 2*n (mod phi(m)) or 0 if no solution exists.

1, 5, 24, 22, 21, 40, 48, 136, 110, 90, 88, 656, 102, 80, 96, 68, 55, 464, 65, 117, 91, 116, 85, 272, 95, 148, 133, 164, 115, 160, 147, 333, 247, 212, 145, 243968, 155, 244, 217, 405, 230, 11072, 185, 292, 259, 1184, 205, 237824, 215, 657, 301, 356, 189, 343, 329, 388, 559, 404

Offset

0,2

Comments

a(221) <= 288230257234804736 = 2^(k-2)*(2^k-443) for k=30. - Michel Marcus, Apr 02 2020

a(221) > 10^13. - Giovanni Resta, Apr 12 2020

Links

Michel Marcus, Table of n, a(n) for n = 0..220

Prog

(PARI) g(n) = my(f=factor(n)); sigma(f) % eulerphi(f);
a(n) = {n *= 2; my(k=1); while (g(k) != n, k++); k; } \\ Michel Marcus, Mar 30 2020

Crossrefs

Bisection of A072808.

Cf. A000203, A000010, A063514, A067192, A067193.

Sequence in context: A200822 A112613 A305057 * A222355 A335352 A056234

Adjacent sequences: A333630 A333631 A333632 * A333634 A333635 A333636

Keyword

nonn

Author

Michel Marcus, Mar 30 2020

Extensions

a(0) prepended by Jinyuan Wang, Mar 30 2020

Status

approved