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A003679 Numbers that are not the sum of 3 pentagonal numbers.
(Formerly M3323)
8
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; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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, Apr 19 2006

REFERENCES

R. K. Guy, Every number is expressible as the sum of how many polygonal numbers?, Amer. Math. Monthly 101 (1994), 169-172.

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n = 1..210

Eric Weisstein's World of Mathematics, Pentagonal Number

MATHEMATICA

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, Apr 19 2006

CROSSREFS

Cf. A117065 (primes in this sequence).

Cf. A118278, A118279.

Sequence in context: A166402 A034038 A069265 * A079432 A162215 A134344

Adjacent sequences:  A003676 A003677 A003678 * A003680 A003681 A003682

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane, Mira Bernstein

STATUS

approved

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Last modified December 20 08:42 EST 2014. Contains 252241 sequences.