A204464 Number of 2*n-element subsets that can be chosen from {1,2,...,16*n} having element sum n*(16*n+1).

1, 8, 790, 148718, 35154340, 9408671330, 2725410001024, 834014033203632, 265724127467961324, 87318355216835049968, 29402690636348418710858, 10098693807141197229592054, 3525753285145412581617963136, 1248001014165722671454730108968, 446964111600452023289482445527716

Offset: 0

Author

Alois P. Heinz, Jan 18 2012

Keywords

• nonn

Comments

a(n) is the number of partitions of n*(16*n+1) into 2*n distinct parts <=16*n.

Examples

			a(1) = 8 because there are 8 2-element subsets that can be chosen from {1,2,...,16} having element sum 17: {1,16}, {2,15}, {3,14}, {4,13}, {5,12}, {6,11}, {7,10}, {8,9}.
		

Crossrefs

Bisection of row n=8 of A204459.

Programs

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*(16*n+1), 16*n, 2*n):
seq(a(n), n=0..10);

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[nJean-François Alcover, Dec 07 2020, after Alois P. Heinz *)