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Search: id:A064322
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| A064322 |
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Triply triangular numbers. |
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+0
4
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| 0, 1, 21, 231, 1540, 7260, 26796, 82621, 222111, 536130, 1186570, 2445366, 4747821, 8763391, 15487395, 26357430, 43398586, 69401871, 108140571, 164629585, 245433090, 359026206, 516216646, 730632651, 1019283825
(list; graph; listen)
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OFFSET
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0,3
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LINKS
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Harry J. Smith, Table of n, a(n) for n=0,...,400
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FORMULA
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a(n) = A000217(A000217(A000217(n))) = n*(n+1)*(n^2+n+2)*(n^4+2n^3+n^2+2n^2+2n+8)/128 = A002817(n)*(A002817(n)+1)/2
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EXAMPLE
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a(4)=1540 because 4th triangular number is 10, 10th triangular number is 55 and 55th triangular number is 1540.
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MATHEMATICA
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f[n_] := n(n + 1)/2; Table[ Nest[f, n, 3], {n, 0, 25}] (from Robert G. Wilson v Jun 30 2004)
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PROGRAM
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(PARI) Tri(n)= { n*(n + 1)/2 } { for (n=0, 400, write("b064322.txt", n, " ", Tri(Tri(Tri(n)))) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Sep 11 2009]
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CROSSREFS
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Cf. A000217, A002817, A066370.
Sequence in context: A027812 A027508 A020267 this_sequence A126902 A010973 A022586
Adjacent sequences: A064319 A064320 A064321 this_sequence A064323 A064324 A064325
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KEYWORD
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nonn
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AUTHOR
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Henry Bottomley (se16(AT)btinternet.com), Oct 15 2001
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