A075764 Schroeder pseudoprimes: Composites k that divide the k-th Schroeder number A001003(k-1).

105, 261, 301, 693, 1605, 1755, 2151, 2905, 2907, 3393, 3875, 4641, 4833, 5005, 5655, 6279, 6913, 7161, 8883, 9405, 10899, 11025, 11289, 15687, 17199, 19203, 22275, 27387, 36855, 37791, 50007, 50463, 53493, 54891, 55209, 55755, 63327, 64337

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..422

Example

105 is a term because A001003(105) = 15646506064359350392347086201481965698808674470977505246623827696393838448345 which is divisible by 105.
105 is a term because A001003(104) = 15646506064359350392347086201481965698808674470977505246623827696393838448345 which is divisible by 105.

Mathematica

s = {}; k1 = k2 = 1; Do[k3 = ((6*n - 9)*k2 - (n - 3)*k1)/n; If[CompositeQ[n] && Divisible[k3, n], AppendTo[s, n]]; k1 = k2; k2 = k3, {n, 3, 10^5}]; s (* Amiram Eldar, Jun 28 2022 *)

Prog

(PARI) x1 = 1; x2 = 1; for (n = 3, 100000, x = (3*(2*n - 3)*x1 - (n - 3)*x2)/n; if (!isprime(n), if (!(x%n), print(n))); x2 = x1; x1 = x); \\ David Wasserman, Feb 23 2005

Crossrefs

Intersection of A002808 and A075763.

Cf. A001003, A013998, A075762.

Sequence in context: A250757 A350199 A146257 * A046299 A010090 A306122

Adjacent sequences: A075761 A075762 A075763 * A075765 A075766 A075767

Keyword

nonn

Author

Benoit Cloitre, Oct 09 2002

Extensions

More terms from David Wasserman, Feb 23 2005

Status

approved