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Numbers k that divide the k-th NSW number.
0

%I #5 May 18 2024 01:49:25

%S 1,7,217,3937,6727,6847,51943,170671,330337,385687,2484247,2566537,

%T 2904007,3020857,3696967,6465577,9405337,12021439,19384207

%N Numbers k that divide the k-th NSW number.

%C Numbers k such that k | A002315(k).

%e 7 is a term since A002315(7) = 275807 = 7 * 39401 is divisible by 7.

%t seq[kmax_] := Module[{nsw0 = 1, nsw1 = 7, nsw2, s = {1}}, Do[nsw2 = 6*nsw1 - nsw0; If[Divisible[nsw2, k], AppendTo[s, k]]; nsw0 = nsw1; nsw1 = nsw2, {k, 2, kmax}]; s]; seq[52000]

%o (PARI) lista(kmax) = {my(nsw0 = 1, nsw1 = 7, nsw2); print1("1, "); for(k = 2, kmax, nsw2 = 6*nsw1 - nsw0; if(!(nsw2 % k), print1(k, ", ")); nsw0 = nsw1; nsw1 = nsw2);}

%Y Cf. A002315, A330276.

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

%K nonn,more

%O 1,2

%A _Amiram Eldar_, May 17 2024