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a(n) = A258220(2n,n).
2

%I #12 Mar 17 2024 05:42:57

%S 1,6,217,13997,1283817,151778430,21902350480,3726598826676,

%T 729894290301789,161683308639785288,39960246577221138239,

%U 10900687898284398341055,3253179971490906621196740,1054372896576358319473872858,368810384314446516250937494104

%N a(n) = A258220(2n,n).

%H Vaclav Kotesovec, <a href="/A292692/b292692.txt">Table of n, a(n) for n = 0..290</a> (terms 0..200 from Alois P. Heinz)

%F a(n) ~ c * d^n * n! / sqrt(n), where d = 25.81959672662517201... and c = 0.28310309251343879... - _Vaclav Kotesovec_, Dec 01 2017

%F Conjecture: d = (51*sqrt(17) - 107)/4. - _Vaclav Kotesovec_, Mar 17 2024

%Y Cf. A258220.

%K nonn

%O 0,2

%A _Alois P. Heinz_, Sep 20 2017