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A125201
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a(n) = 8*n^2 - 7*n + 1.
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2
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2, 19, 52, 101, 166, 247, 344, 457, 586, 731, 892, 1069, 1262, 1471, 1696, 1937, 2194, 2467, 2756, 3061, 3382, 3719, 4072, 4441, 4826, 5227, 5644, 6077, 6526, 6991, 7472, 7969, 8482, 9011, 9556, 10117, 10694, 11287, 11896, 12521, 13162, 13819, 14492, 15181
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OFFSET
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1,1
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COMMENTS
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Central terms of the triangle in A125199.
Sequence found by reading the line from 2, in the direction 2, 19, ..., in the square spiral whose vertices are the triangular numbers A000217. - Omar E. Pol, Sep 05 2011
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LINKS
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FORMULA
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a(n) = 1 + A051870(n). - Omar E. Pol, Sep 05 2011
a(1) = 2, a(n) = a(n-1) + 16*n - 15.
a(n) = 2*a(n-1) - a(n-2) + 16 with a(1) = 2 and a(2) = 19.
G.f.: (1 - x + 16*x^2)/(1 - x)^3. (End)
Sum_{n>=1} 1/a(n) = ( psi(9/16+sqrt(17)/16) -psi(9/16-sqrt(17)/16)) /sqrt(17) = 0.61242052... - R. J. Mathar, Apr 22 2024
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MATHEMATICA
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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