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A333633
Smallest m such that sigma(m) == 2*n (mod phi(m)) or 0 if no solution exists.
1
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
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.
Sequence in context: A200822 A112613 A305057 * A222355 A335352 A056234
KEYWORD
nonn
AUTHOR
Michel Marcus, Mar 30 2020
EXTENSIONS
a(0) prepended by Jinyuan Wang, Mar 30 2020
STATUS
approved