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A082658
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Integers expressible as the sum of a square and a triangular number in exactly two distinct ways.
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4
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7, 15, 22, 26, 28, 31, 40, 45, 52, 55, 59, 61, 67, 79, 85, 87, 92, 94, 100, 102, 103, 106, 114, 115, 124, 130, 140, 142, 147, 155, 157, 159, 166, 175, 178, 180, 184, 187, 189, 190, 191, 197, 202, 205, 206, 210, 211, 214, 220, 224, 231, 232, 240, 241, 246, 247
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OFFSET
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1,1
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COMMENTS
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It is assumed here that 0 is a square but not a triangular number. - Amiram Eldar, Dec 08 2019
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LINKS
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Amiram Eldar, Table of n, a(n) for n = 1..10000
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EXAMPLE
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a(4) = 26 because 26 = 1 + 25; 26 = 10 + 16.
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MATHEMATICA
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aQ[n_] := Length @ Solve[x^2 + y (y + 1)/2 == n && x >= 0 && y > 0, {x, y}, Integers] == 2; Select[Range[250], aQ] (* Amiram Eldar, Dec 08 2019 *)
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CROSSREFS
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Cf. A000217, A000290, A082657, A082659, A082660.
Sequence in context: A346197 A274700 A022552 * A022389 A041225 A128840
Adjacent sequences: A082655 A082656 A082657 * A082659 A082660 A082661
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KEYWORD
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nonn
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AUTHOR
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Jason Earls, May 17 2003
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EXTENSIONS
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Name clarified by Amiram Eldar, Dec 08 2019
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STATUS
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approved
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