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A076768
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Integers not expressible as the sum of a prime and a triangular number.
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9
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1, 36, 105, 171, 210, 216, 325, 351, 406, 528, 561, 630, 741, 780, 990, 1081, 1176, 1275, 1596, 1711, 1830, 1953, 2016, 2145, 2346, 2628, 2775, 3003, 3081, 3240, 3321, 3655, 3741, 3916, 4278, 4371, 4465, 4560, 4851, 5253, 5460, 5565, 5886, 6105, 6216, 6786, 7021, 7140, 7503, 7626, 7750, 7875, 8256, 8515, 8911, 9045, 9591, 9870
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| It appears that 1,2,3,8 are the only positive integers that cannot be partitioned as the sum of a semiprime and a triangular number. Here triangular numbers include t(0)=0 and t(1)=1. - Jonathan Vos Post (jvospost3(AT)gmail.com) and Ray Chandler (rayjchandler(AT)sbcglobal.net), Nov 28 2004
This sequence contains 216 (and possibly other nontriangular numbers) together with an infinite number of triangular numbers. The indices of the triangular numbers are in A138666. This is related to the Sun's conjecture (see A132399) that every number except 216 is the sum of a triangular number and a prime or 0. - T. D. Noe (noe(AT)sspectra.com), Mar 26 2008
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LINKS
| T. D. Noe, Table of n, a(n) for n=1..1001
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EXAMPLE
| a(2) = 36 is an element of this sequence because 36 cannot be written as a sum of one of the primes <= 36 {2,3,5,7,11,13,17,19,23,29,31} and one of the triangular numbers <= 36 {1,3,6,10,15,21,36}.
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CROSSREFS
| Cf. A000040, A000217, A046903.
Sequence in context: A163246 A014738 A182677 * A162940 A176685 A199260
Adjacent sequences: A076765 A076766 A076767 * A076769 A076770 A076771
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Nov 14 2002
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EXTENSIONS
| Nov 28 2004: Jonathan Vos Post (jvospost3(AT)gmail.com) and Ray Chandler (rayjchandler(AT)sbcglobal.net) added the terms 6786 through 9870 and conjecture that there are no further terms.
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