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A364610
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Centered pentagonal numbers which are products of three distinct primes (or sphenic numbers).
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0
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1266, 1626, 2806, 3706, 4731, 6126, 7426, 7701, 9766, 10726, 13506, 15801, 18706, 19581, 25251, 26266, 26781, 31641, 35106, 36906, 40006, 50766, 52926, 56626, 57381, 62806, 69306, 71826, 74391, 76126, 85101, 90726, 93606, 95551, 96531, 99501, 106606, 108681, 109726, 117181, 121551, 123766
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OFFSET
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1,1
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LINKS
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EXAMPLE
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A005891(22) = 1266 = (5*22^2 + 5*22 + 2)/2 = 2 * 3 * 211.
A005891(25) = 1626 = (5*25^2 + 5*25 + 2)/2 = 2 * 3 * 271.
A005891(33) = 2806 = (5*33^2 + 5*33 + 2)/2 = 2 * 23 * 61.
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MATHEMATICA
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Select[Table[5*n*(n + 1)/2 + 1, {n, 0, 225}], FactorInteger[#][[;; , 2]] == {1, 1, 1} &] (* Amiram Eldar, Sep 07 2023 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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