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A135756
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a(n) = Sum_{k=0..n} C(n,k) * 2^(k*(k-1)).
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4
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1, 2, 7, 80, 4381, 1069742, 1080096067, 4405584869660, 72092808533798521, 4723015159635987920282, 1237987266193328694390243007, 1298087832233881093828346620725800
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OFFSET
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0,2
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COMMENTS
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The square root of the g.f. of this sequence is an integer series (cf. A261594).
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LINKS
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FORMULA
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EXAMPLE
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G.f.: A(x) = 1 + 2*x + 7*x^2 + 80*x^3 + 4381*x^4 + 1069742*x^5 +...
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MATHEMATICA
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Table[Sum[Binomial[n, k]*2^(2*Binomial[k, 2]), {k, 0, n}], {n, 0, 25}] (* G. C. Greubel, Nov 07 2016 *)
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PROG
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(PARI) {a(n)=sum(k=0, n, binomial(n, k)*2^(k*(k-1)))}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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