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Search: id:A003679
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| A003679 |
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Numbers that are not the sum of 3 pentagonal numbers.
(Formerly M3323)
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+0
7
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| 4, 8, 9, 16, 19, 20, 21, 26, 30, 31, 33, 38, 42, 43, 50, 54, 55, 60, 65, 67, 77, 81, 84, 88, 89, 90, 96, 99, 100, 101, 111, 112, 113, 120, 125, 131, 135, 138, 142, 154, 159, 160, 166, 170, 171, 183, 195, 204, 205, 207, 217, 224, 225, 226, 229, 230, 236, 240, 241
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Guy's paper says that the sequence probably contains exactly 210 terms, six of which require five pentagonal numbers: 9, 21, 31, 43, 55 and 89. The last term is conjectured to be 33066. - T. D. Noe (noe(AT)sspectra.com), Apr 19 2006
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172.
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LINKS
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T. D. Noe, Table of n, a(n) for n = 1..210
Eric Weisstein's World of Mathematics, Pentagonal Number
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MATHEMATICA
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nn=200; pen=Table[n(3n-1)/2, {n, 0, nn-1}]; lst=Range[pen[[ -1]]; Do[n=pen[[i]]+pen[[j]]+pen[[k]]; If[n<=pen[[ -1]], lst=DeleteCases[lst, n]]], {i, nn}, {j, i, nn}, {k, j, nn}]; lst - T. D. Noe (noe(AT)sspectra.com), Apr 19 2006
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CROSSREFS
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Cf. A117065 (primes in this sequence).
Sequence in context: A166402 A034038 A069265 this_sequence A079432 A162215 A134344
Adjacent sequences: A003676 A003677 A003678 this_sequence A003680 A003681 A003682
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KEYWORD
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nonn,easy,nice
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein
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