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A218036
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a(n) = (n+1) + (n+3/2)*H(n) - (H(n)^3)/2, where H(n)=A002024(n).
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0
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4, 6, 9, 8, 12, 16, 10, 15, 20, 25, 12, 18, 24, 30, 36, 14, 21, 28, 35, 42, 49, 16, 24, 32, 40, 48, 56, 64, 18, 27, 36, 45, 54, 63, 72, 81, 20, 30, 40, 50, 60, 70, 80, 90, 100, 22, 33, 44, 55, 66, 77, 88, 99, 110, 121, 24, 36, 48, 60, 72, 84, 96, 108, 120
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OFFSET
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1,1
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COMMENTS
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All terms are composite.
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LINKS
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FORMULA
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As a triangle: T(n, k) = (k + 1)*(n + 1) with 1 <= k <= n. - Stefano Spezia, Nov 23 2019
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EXAMPLE
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Sequence can be seen as a triangle that begins:
4;
6, 9;
8, 12, 16;
10, 15, 20, 25;
12, 18, 24, 30, 36;
14, 21, 28, 35, 42, 49;
16, 24, 32, 40, 48, 56, 64;
...
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MATHEMATICA
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Table[(k+1)*(n+1), {n, 1, 11}, {k, 1, n}]//Flatten (* Stefano Spezia, Nov 23 2019 *)
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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