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A133929
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Positive integers that cannot be expressed using four pentagonal numbers.
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2
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OFFSET
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1,1
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COMMENTS
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Equivalently, integers m such that the smallest number of pentagonal numbers (A000326) which sum to m is exactly five, that is, A100878(a(n)) = 5. Richard Blecksmith & John Selfridge found these six integers among the first million, they believe that they have found them all (Richard K. Guy reference). - Bernard Schott, Jul 22 2022
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REFERENCES
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Richard K. Guy, Unsolved Problems in Number Theory, 3rd Edition, Springer, 2004, Section D3, Figurate numbers, pp. 222-228.
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LINKS
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EXAMPLE
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9 = 5 + 1 + 1 + 1 + 1.
21 = 5 + 5 + 5 + 5 + 1.
31 = 12 + 12 + 5 + 1 + 1.
43 = 35 + 5 + 1 + 1 + 1.
55 = 51 + 1 + 1 + 1 + 1.
89 = 70 + 12 + 5 + 1 + 1.
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CROSSREFS
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KEYWORD
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nonn,fini
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AUTHOR
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STATUS
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approved
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