A233929 Smallest x such that sigma(x) == n-1 (mod n).

1, 1, 7, 2, 3, 2401, 5, 4, 7, 18, 21, 9604, 6, 9, 13, 8, 44, 21609, 10, 18, 19, 289, 36, 9604, 14, 162, 57, 72, 12, 2614689, 29, 16, 21, 625, 63, 38416, 22, 4608, 37, 18, 27, 21609, 20, 289, 43, 36, 50, 38416, 33, 196, 111, 162, 157, 28561, 34, 1296, 28, 49

Offset: 1

Author

Michel Marcus, Dec 18 2013

Keywords

• nonn

Comments

Right subdiagonal of A074625.

Records values are: 1, 7, 2401, 9604, 21609, 2614689, 21215236, 36324729, 53304601, 338964921, 431642176, 528264256, 1307979556, ... obtained at indices: 1, 3, 6, 12, 18, 30, 60, 210, 288, 384, 534, 630, 732. - Michel Marcus, Dec 22 2013

Links

• Michel Marcus and Donovan Johnson, Table of n, a(n) for n = 1..3000 (first 800 terms from Michel Marcus)

Crossrefs

Cf. A000203, A070982, A074625.

Programs

PARI

a(n) = {x = 1; while ((sigma(x) % n) != (n - 1), x++); x;} \\ Michel Marcus, Dec 18 2013