A081730 Numbers k such that the k-th Euler number == 1 (mod k).

1, 2, 3, 4, 5, 7, 8, 11, 13, 15, 16, 17, 19, 23, 29, 31, 32, 37, 41, 43, 47, 53, 59, 61, 64, 67, 71, 73, 79, 83, 89, 91, 97, 101, 103, 107, 109, 113, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241

Offset

1,2

Comments

All primes and all powers of 2 are in the sequence. The composite terms that are not powers of 2 are in A035163.

Links

Amiram Eldar, Table of n, a(n) for n = 1..2000

Mathematica

Select[Range[250], Divisible[Abs[EulerE[2*#]] - 1, #] &] (* Amiram Eldar, Apr 22 2025 *)

Prog

(PARI) a000364(n)=subst(bernpol(2*n+1), 'x, 1/4)*4^(2*n+1)*(-1)^(n+1)/(2*n+1);
lista(nn) = {for (n=1, nn, if (Mod(a000364(n), n) == 1, print1(n, ", ")); ); } \\ Michel Marcus, Apr 18 2015

Crossrefs

Union of A035163 and A174090.

Cf. A000079, A000364, A065091, A069042.

Sequence in context: A241912 A269870 A307824 * A162408 A348284 A162721

Adjacent sequences: A081727 A081728 A081729 * A081731 A081732 A081733

Keyword

nonn

Author

Benoit Cloitre, Apr 06 2003

Extensions

More terms from Weston Markham (weston.markham(AT)gmail.com), May 22 2005

Status

approved