This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A372901 #7 May 17 2024 01:45:08
%S A372901 1,3,9,21,27,81,171,189,217,243,297,351,729,903,1547,2187,3591,3661,
%T A372901 4131,5499,5967,6019,6561,7533,8001,11997,13203,14217,15309,17181,
%U A372901 19683,20601,22113,22599,23529,24297,25659,26163,26319,26487,28441,30051,33021,37179,37791
%N A372901 Numbers k that divide the k-th central Delannoy number.
%C A372901 Numbers k such that k | A001850(k).
%H A372901 Amiram Eldar, <a href="/A372901/b372901.txt">Table of n, a(n) for n = 1..307</a>
%e A372901 3 is a term since A001850(3) = 63 = 3 * 21 is divisible by 3.
%e A372901 9 is a term since A001850(9) = 1462563 = 9 * 162507 is divisible by 9.
%t A372901 Select[Range[1000], Divisible[LegendreP[#, 3], #] &]
%o A372901 (PARI) lista(kmax) = {my(cd0 = 1, cd1 = 3, cd2); print1("1, "); for(k = 2, kmax, cd2 = (3*(2*k-1)*cd1 - (k-1)*cd0)/k; if(!(cd2 % k), print1(k, ", ")); cd0 = cd1; cd1 = cd2);}
%Y A372901 Cf. A001850.
%Y A372901 Similar sequences: A014847 (Catalan), A016089 (Lucas), A023172 (Fibonacci), A051177 (partition), A232570 (tribonacci), A246692 (Pell), A266969 (Motzkin).
%K A372901 nonn
%O A372901 1,2
%A A372901 _Amiram Eldar_, May 16 2024