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A185003
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a(n) = Sum_{k=1..n} binomial(n,k)*sigma(k).
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15
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1, 5, 16, 45, 116, 284, 673, 1557, 3535, 7910, 17502, 38376, 83500, 180479, 387881, 829605, 1766998, 3749765, 7931114, 16724870, 35173777, 73794660, 154485527, 322771344, 673155141, 1401536934, 2913490375, 6047714599, 12536770558, 25956242579, 53678385266
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OFFSET
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1,2
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LINKS
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FORMULA
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Logarithmic derivative of A103446 (with offset=0), which describes the binomial transform of partitions.
L.g.f.: Sum_{n>=1} sigma(n) * x^n/(1-x)^n / n.
L.g.f.: Sum_{n>=1} x^n/((1-x)^n - x^n) / n.
L.g.f.: Sum_{n>=1} n*log(1-x) - log((1-x)^n - x^n).
L.g.f.: Sum_{n>=1} A001511(n) * log(1 + x^n/(1-x)^n), where 2^A001511(n) is the highest power of 2 that divides 2*n.
a(n) = Sum_{i=1..n} Sum_{j=1..n} i*binomial(n,i*j). - Ridouane Oudra, Nov 12 2019
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EXAMPLE
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L.g.f.: L(x) = x + 5*x^2/2 + 16*x^3/3 + 45*x^4/4 + 116*x^5/5 + 284*x^6/6 +...
where exponentiation yields A103446 (with offset=0):
exp(L(x)) = 1 + x + 3*x^2 + 8*x^3 + 21*x^4 + 54*x^5 + 137*x^6 + 344*x^7 +...
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MAPLE
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with(numtheory): seq(add(binomial(n, i)*sigma(i), i=1..n), n=1..40); # Ridouane Oudra, Nov 12 2019
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MATHEMATICA
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Table[Sum[Binomial[n, k] DivisorSigma[1, k], {k, n}], {n, 50}] (* G. C. Greubel, Jun 03 2017 *)
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PROG
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(PARI) {a(n)=sum(k=1, n, sigma(k)*binomial(n, k))}
for(n=1, 30, print1(a(n), ", "))
(PARI) {a(n)=local(X=x+x*O(x^n)); n*polcoeff(sum(m=1, n+1, x^m/((1-x)^m-X^m)/m), n)}
(PARI) {a(n)=local(X=x+x*O(x^n)); n*polcoeff(sum(k=1, n, k*log(1-X)-log((1-x)^k-X^k)), n)}
(PARI) {a(n)=local(X=x+x*O(x^n)); n*polcoeff(sum(m=1, n+1, sigma(m)*x^m/(1-X)^m/m), n)}
(PARI) {a(n)=local(X=x+x*O(x^n)); n*polcoeff(sum(k=1, n, valuation(2*k, 2)*log(1 + x^k/(1-X)^k)), n)}
(Magma) [&+[Binomial(n, k)*DivisorSigma(1, k):k in [1..n]]:n in [1..31]]; // Marius A. Burtea, Nov 12 2019
(Magma) [&+[&+[i*Binomial(n, i*j):j in [1..n]]:i in [1..n]]:n in [1..31]]; // Marius A. Burtea, Nov 12 2019
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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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