A371779 a(n) = Sum_{k=0..floor(n/3)} binomial(4*n+2,n-3*k).
1, 6, 45, 365, 3078, 26565, 232831, 2063235, 18435021, 165780758, 1498533273, 13603087800, 123920995101, 1132284232215, 10372554403620, 95233251146671, 876081280823430, 8073359613286509, 74513645742072841, 688682977876117698, 6373025238727622277
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=0, n\3, binomial(4*n+2, n-3*k));
Formula
a(n) = [x^n] 1/(((1-x)^3-x^3) * (1-x)^(3*n)).