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A107881 Column 0 of triangle A107880. 4
1, 2, 3, 7, 26, 141, 1034, 9693, 111522, 1528112, 24372513, 444461496, 9135985760, 209223309377, 5286985099830, 146225910921737, 4395973641599418, 142794782804641965, 4985911547339049132, 186284207595651780174 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..19.

FORMULA

G.f.: 1 = Sum_{k>=0} a(k)*x^k*(1-x)^(2 + k*(k-1)/2).

EXAMPLE

1 = 1*(1-x)^2 + 2*x*(1-x)^2 + 3*x^2*(1-x)^3 +

7*x^3*(1-x)^5 + 26*x^4*(1-x)^8 + 141*x^5*(1-x)^12 +...

PROG

(PARI) {a(n)=polcoeff(1-sum(k=0, n-1, a(k)*x^k*(1-x+x*O(x^n))^(2+k*(k-1)/2)), n)}

CROSSREFS

Cf. A107880, A107882, A107883.

Sequence in context: A308114 A092983 A089708 * A128001 A264829 A156142

Adjacent sequences:  A107878 A107879 A107880 * A107882 A107883 A107884

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 04 2005

STATUS

approved

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Last modified June 16 13:31 EDT 2019. Contains 324152 sequences. (Running on oeis4.)