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A120536
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Semiprimes which are the sum of two pentagonal numbers (A000326) in exactly two different ways.
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0
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215, 381, 447, 766, 807, 1457, 1622, 1639, 1927, 2047, 2245, 2302, 2497, 3027, 3173, 3437, 3715, 3787, 4359, 4369, 4577, 4594, 4677, 4681, 5029, 5277, 5377, 5435, 5617, 5747, 5911, 6065, 6117, 6537, 6711, 6722, 6782, 7087, 7157, 7327, 7538, 7661, 7813, 7827
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OFFSET
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1,1
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COMMENTS
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Semiprimes in A064826 Numbers which are the sum of two pentagonal numbers (A000326) in exactly two different ways.
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LINKS
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MATHEMATICA
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T = Range[10^4]*0; q = # (3 # - 1)/2 &@ Range[81]; Do[ s = q[[i]] + q[[j]]; If[s <= 10^4, T[[s]]++], {i, Length[q]}, {j, i}]; Select[ Flatten@ Position[T, 2], PrimeOmega[#] == 2 &] (* Giovanni Resta, Jun 13 2016 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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