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A224247
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G.f.: Sum_{n>=1} x^n*(1+x)^d(n), where d(n) is the number of divisors of n (A000005).
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1
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1, 2, 3, 4, 5, 6, 7, 9, 10, 11, 12, 11, 12, 19, 26, 26, 22, 19, 19, 23, 29, 35, 37, 29, 21, 34, 64, 82, 73, 51, 39, 47, 70, 91, 87, 58, 35, 46, 91, 137, 145, 120, 103, 110, 121, 120, 104, 73, 45, 58, 131, 231, 285, 247, 157, 94, 87, 109, 124, 111, 83, 99, 234, 509
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OFFSET
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1,2
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LINKS
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EXAMPLE
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G.f.: A(x) = x + 2*x^2 + 3*x^3 + 4*x^4 + 5*x^5 + 6*x^6 + 7*x^7 + 9*x^8 +...
where
A(x) = x*(1+x) + x^2*(1+x)^2 + x^3*(1+x)^2 + x^4*(1+x)^3 + x^5*(1+x)^2 + x^6*(1+x)^4 + x^7*(1+x)^2 + x^8*(1+x)^4 + x^9*(1+x)^3 + x^10*(1+x)^4 + x^11*(1+x)^2 + x^12*(1+x)^6 +...
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PROG
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(PARI) {a(n)=polcoeff(sum(k=1, n, x^k*(1+x)^sigma(k, 0))+x*O(x^n), n)}
for(n=1, 70, print1(a(n), ", "))
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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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