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A274233
Number of partitions of n*(n-1)/2 into at most three parts.
2
1, 1, 3, 7, 14, 27, 48, 80, 127, 192, 280, 397, 547, 736, 972, 1261, 1610, 2028, 2523, 3104, 3781, 4563, 5461, 6487, 7651, 8965, 10443, 12097, 13940, 15987, 18252, 20750, 23497, 26508, 29800, 33391, 37297, 41536, 46128, 51091, 56444, 62208, 68403, 75050
OFFSET
1,3
LINKS
FORMULA
Coefficient of x^(n*(n-1)/2) in 1/((1-x)*(1-x^2)*(1-x^3)).
Empirical g.f.: (1-3*x+6*x^2-7*x^3+9*x^4-7*x^5+6*x^6-3*x^7+x^8) / ((1-x)^5*(1+x^2)*(1+x+x^2)).
PROG
(PARI)
\\ b(n) is the coefficient of x^n in the g.f. 1/((1-x)*(1-x^2)*(1-x^3)).
b(n) = round(real((47+9*(-1)^n + 8*exp(-2/3*I*n*Pi) + 8*exp((2*I*n*Pi)/3) + 36*n+6*n^2)/72))
vector(50, n, b(n*(n-1)/2))
CROSSREFS
A subsequence of A001399. Cf. A274099, A274232.
Sequence in context: A117071 A019459 A276024 * A369576 A256209 A236914
KEYWORD
nonn
AUTHOR
Colin Barker, Jun 15 2016
STATUS
approved