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A152950
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a(n) = 3 + n*(n-1)/2.
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16
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3, 4, 6, 9, 13, 18, 24, 31, 39, 48, 58, 69, 81, 94, 108, 123, 139, 156, 174, 193, 213, 234, 256, 279, 303, 328, 354, 381, 409, 438, 468, 499, 531, 564, 598, 633, 669, 706, 744, 783, 823, 864, 906, 949, 993, 1038, 1084, 1131, 1179, 1228, 1278, 1329, 1381, 1434
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OFFSET
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1,1
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COMMENTS
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a(1)=3; then add 1 to the first number, then 2,3,4... and so on.
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LINKS
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FORMULA
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Sum_{n>=1} 1/a(n) = 2*Pi*tanh(sqrt(23)*Pi/2)/sqrt(23). - Amiram Eldar, Dec 13 2022
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MAPLE
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MATHEMATICA
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s=3; lst={3}; Do[s+=n; AppendTo[lst, s], {n, 1, 5!}]; lst
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PROG
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(Sage) [3+binomial(n, 2) for n in range(1, 55)] # Zerinvary Lajos, Mar 12 2009
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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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