A035163 -id:A035163 - cp's OEIS frontend

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

Benoit Cloitre, Apr 06 2003

nonn

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

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

Union of A035163 and A174090.

Cf. A000079, A000364, A065091, A069042.

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

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

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

A287934 Composite numbers n such that E(n+1)+1 is divisible by n, where E(n) is the n-th Euler number (A122045).

Original entry on oeis.org

289, 341, 561, 1105, 1369, 1387, 1729, 2465, 2821, 4097, 5365, 6179, 6601, 8911, 9105, 9537, 10585, 12673, 14433, 14531, 15457, 15841, 28033, 29341, 33901, 41041, 41905, 42141, 46657, 48705, 52633, 52741, 62745, 63253, 63973, 75361, 80185, 82621, 99937

Offset: 1

Amiram Eldar, Jun 03 2017

nonn

Kummer proved in 1851 that E(2k + p - 1) == E(2k) (mod p) for k > 0 and all odd primes p. This sequence consists of composite numbers for which the congruence, with k=1, also holds. In terms of A000364, the sequence consists of composite odd numbers n that divide A000364((n + 1)/2) + (-1)^((n + 1)/2).

Jozsef Sandor and Borislav Crstici, Handbook of Number theory II, Kluwer Academic Publishers, 2004, Chapter 5, p. 556.

Leonard Carlitz, Congruences for generalized Bell and Stirling numbers, Duke Mathematical Journal, Vol. 22, No. 2 (1955), pp. 193-205.
Ernst Eduard Kummer, Über eine allgemeine Eigenschaft der rationalen Entwickelungscoefficienten einer bestimmten Gattung analytischer Functionen, Journal für die reine und angewandte Mathematik, Vol. 41 (1851), pp. 368-372.
Samuel S. Wagstaff, Jr., Prime divisors of the Bernoulli and Euler numbers, Number Theory for the Millenium III (Urbana, IL, 2000), AK Peters, Natick, MA, 2002, pp. 357-374.

Cf. A000364, A035163, A081730, A122045, A180942.

a={}; For[n = 1, n < 100000, n++; If[!PrimeQ[n] && Divisible[EulerE[n + 1] + 1, n], a=AppendTo[a,n]]];a
Select[Range[100000],CompositeQ[#]&&Divisible[EulerE[#+1]+1,#]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 03 2019 *)

e(n) = 2^n*2^(n+1)*(subst(bernpol(n+1, x), x, 3/4) - subst(bernpol(n+1, x), x, 1/4))/(n+1);
isok(n) = (((e(n+1)+1) % n) == 0);
lista(nn) = forcomposite(n=1, nn, if (isok(n), print1(n, ", "))); \\ Michel Marcus, Jun 10 2017

cp's OEIS Frontend

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

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