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A126152
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Main diagonal of symmetric triangle A126150: a(n) = A126150(n,n).
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4
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1, 4, 36, 744, 28536, 1736064, 152914176, 18372559104, 2885671339776, 573765893121024, 140835811776316416, 41820352964911908864, 14774712204104658671616, 6124078747943873540112384
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| a(n)=Sum_{k, 0<=k<=n}A130847(n,k)*3^k. - Philippe DELEHAM (kolotoko(AT)wanadoo.fr), Jul 22 2007
G.f.: 1/(1 - 4*x/(1-5*x/(1 - 21*x/(1-22*x/(1 - 50*x/(1-51*x/(1 - 91*x/(1-92*x/(1 -...)))))))))))), a continued fraction involving even-indexed pentagonal numbers A000326. [From Paul D. Hanna, Feb 15 2012]
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PROG
| (PARI) /* Continued fraction involving even-indexed pentagonal numbers: */
{a(n)=local(CF=1+x*O(x), m, P); for(k=1, n, m=2*((n-k)\2+1); P=m*(3*m-1)/2-((n-k+1)%2); CF=1/(1-P*x*CF)); polcoeff(CF, n, x)}
for(n=0, 20, print1(a(n), ", "))
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CROSSREFS
| Cf. A126150; A126151 (column 0), A126153 (diagonal).
Sequence in context: A163887 A156630 A145565 * A009446 A134052 A127901
Adjacent sequences: A126149 A126150 A126151 * A126153 A126154 A126155
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KEYWORD
| nonn,changed
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Dec 19 2006
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