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Search: id:A067056
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| A067056 |
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a(n) = (1)*(2+3+4+...+ n) + (1+2)*(3+4+5+...+n) + (1+2+3)*(4+5+6...+ n)+ ...+ Sum(n) or a(n) = Sum { Sum(1 to r) * Sum( r+1 to n)}, r = 1 to n. |
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+0
1
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| 1, 2, 14, 54, 154, 364, 756, 1428, 2508, 4158, 6578, 10010, 14742, 21112, 29512, 40392, 54264, 71706, 93366, 119966, 152306, 191268, 237820, 293020, 358020, 434070, 522522, 624834, 742574, 877424, 1031184, 1205776, 1403248, 1625778
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n) = Sum {t(r)*{ t(n) - t(r) }}, ( r = 1 to n-1) where t(r) is the r-th triangular number.
n(2n^4+5n^3-5n-2)/60 = (n-1)n(n+1)(n+2)(2n+1)/60, n>1. - R. Stephan, Apr 30 2004
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EXAMPLE
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a(4) = (1)*(2+3+4) + (1+2)*(3+4) + (1+2+3)*(4) + = 9+21+24 = 54.
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CROSSREFS
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Adjacent sequences: A067053 A067054 A067055 this_sequence A067057 A067058 A067059
Sequence in context: A056080 A143553 A064363 this_sequence A137482 A115027 A114146
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KEYWORD
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easy,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Jan 02 2002
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EXTENSIONS
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More terms from Jason Earls (zevi_35711(AT)yahoo.com), Jan 11 2002
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