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Search: id:A087115
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| A087115 |
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Convolution of sum of cubes of divisors with itself. |
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+0
2
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| 0, 1, 18, 137, 650, 2350, 6860, 17609, 39870, 83976, 162382, 301070, 522886, 885284, 1424468, 2254537, 3419448, 5143987, 7448874, 10750712, 15015872, 20948610, 28373444, 38539022, 50863150, 67454492, 87209316, 113326308, 143748766, 183759900, 229271536
(list; graph; listen)
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OFFSET
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1,3
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REFERENCES
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J.-P. Serre, A Course in Arithmetic, Springer-Verlag, 1973, Chap. VII, Section 4., p. 93.
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FORMULA
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G.f.: (sum(k>=1, k^3*x^k/(1-x^k)))^2. a(n)=(sigma_7(n)-sigma_3(n))/120.
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MAPLE
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with(numtheory); f:=n->add( sigma[3](k)*sigma[3](n-k), k=1..n-1);
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PROGRAM
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(PARI) a(n)=if(n<1, 0, (sigma(n, 7)-sigma(n, 3))/120)
(PARI) a(n)=if(n<1, 0, sum(m=1, n-1, sigma(m, 3)*sigma(n-m, 3)))
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CROSSREFS
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Cf. A001158, A013955.
Sequence in context: A022710 A056003 A114239 this_sequence A163707 A108680 A081074
Adjacent sequences: A087112 A087113 A087114 this_sequence A087116 A087117 A087118
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KEYWORD
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nonn
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AUTHOR
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Michael Somos, Aug 13 2003
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