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Search: id:A126335
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| 3, 23, 72, 162, 305, 513, 798, 1172, 1647, 2235, 2948, 3798, 4797, 5957, 7290, 8808, 10523, 12447, 14592, 16970, 19593, 22473, 25622, 29052, 32775, 36803, 41148, 45822, 50837, 56205, 61938, 68048, 74547, 81447, 88760, 96498, 104673, 113297
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OFFSET
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1,1
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COMMENT
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Inner product of two arithmetic series: (1,4,7,...,3n-2)*(3,5,7,...,2n+1) = sum((3i-2)*(2i+1),i=1...n) = 1*3+4*3+7*7+...+(3n-2)*(2n+1) = (1/2)*n*(4*n^2+5*n-3).
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FORMULA
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a(1)=3, a(2)=23, a(3)=72, a(4)=162; for n>4, a(n)=4*a(n-1)-6*a(n-2)+4*a(n-3)-a(n-4). G.f. = x*(3 + 11*x - 2*x^2)/(1 - x)^4.
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CROSSREFS
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Sequence in context: A096207 A163210 A163211 this_sequence A027701 A032017 A024196
Adjacent sequences: A126332 A126333 A126334 this_sequence A126336 A126337 A126338
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)gmail.com), Mar 11 2007
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