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 A204461 Number of n-element subsets that can be chosen from {1,2,...,5*n} having element sum n*(5*n+1)/2. 2
 1, 1, 5, 25, 177, 1394, 11963, 108108, 1016737, 9853759, 97809616, 989878326, 10180316707, 106124695130, 1119148085092, 11920389375524, 128077285062639, 1386689101261013, 15115933170815361, 165776800325379769, 1828006462946421194, 20256667860779557632 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n) is the number of partitions of n*(5*n+1)/2 into n distinct parts <=5*n. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..100 EXAMPLE a(2) = 5 because there are 5 2-element subsets that can be chosen from {1,2,...,10} having element sum 11: {1,10}, {2,9}, {3,8}, {4,7}, {5,6}. MAPLE b:= proc(n, i, t) option remember; `if`(it*(2*i-t+1)/2, 0, `if`(n=0, 1, b(n, i-1, t) +`if`(n b(n*(5*n+1)/2, 5*n, n): seq(a(n), n=0..20); MATHEMATICA b[n_, i_, t_] /; it(2i-t+1)/2 = 0; b[0, _, _] = 1; b[n_, i_, t_] := b[n, i, t] = b[n, i-1, t] + If[n

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Last modified May 28 21:07 EDT 2023. Contains 363028 sequences. (Running on oeis4.)