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A370285 Coefficient of x^n in the expansion of ( (1+x)^2 + x^3 )^n. 1
1, 2, 6, 23, 94, 392, 1659, 7107, 30734, 133880, 586576, 2582142, 11411371, 50597900, 224986467, 1002867878, 4479814606, 20049099908, 89878609344, 403521966942, 1814102538624, 8165526187128, 36794746597494, 165968135843522, 749314496125451, 3385881647958442 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
FORMULA
a(n) = Sum_{k=0..floor(n/3)} binomial(n,k) * binomial(2*n-2*k,n-3*k).
The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x / ((1+x)^2 + x^3) ). See A369212.
PROG
(PARI) a(n) = sum(k=0, n\3, binomial(n, k)*binomial(2*n-2*k, n-3*k));
CROSSREFS
Cf. A369212.
Sequence in context: A150292 A191721 A150293 * A371827 A150294 A150295
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 14 2024
STATUS
approved

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Last modified June 23 23:42 EDT 2024. Contains 373661 sequences. (Running on oeis4.)