A372945 Numbers k that divide the k-th Wedderburn-Etherington number.

1, 6, 36, 49, 61, 223, 4258, 9747

Offset

1,2

Comments

Numbers k such that k | A001190(k).

a(9) > 90000, if it exists.

Links

Table of n, a(n) for n=1..8.

Example

6 is a term since A001190(6) = 6 is divisible by 6.
36 is a term since A001190(36) = 249959727972 = 36 * 6943325777 is divisible by 36.

Mathematica

v[0] = 0; v[1] = 1; v[n_] := v[n] = Sum[v[k] * v[n-k], {k, 1, Floor[(n-1)/2]}] + If[EvenQ[n], v[n/2]*(v[n/2]+1)/2, 0]; Select[Range[10^4], Divisible[v[#], #] &]

Prog

(PARI) lista(kmax) = {my(v = vector(kmax, i, 1)); print1(1, ", "); for(k = 4, kmax, v[k] = sum(i = 1, (k-1)\2, v[i] * v[k-i]) + if(!(k % 2), v[k/2] * (v[k/2] + 1)/2); if(!(v[k] % k), print1(k, ", "))); }

Crossrefs

Cf. A001190.

Similar sequences: A014847 (Catalan), A016089 (Lucas), A023172 (Fibonacci), A051177 (partition), A232570 (tribonacci), A246692 (Pell), A266969 (Motzkin).

Sequence in context: A232137 A008460 A132633 * A047792 A178909 A206982

Adjacent sequences: A372942 A372943 A372944 * A372946 A372947 A372948

Keyword

nonn,more

Author

Amiram Eldar, May 17 2024

Status

approved