A281872 Number of sets of exactly n positive integers <= 2n having a square element sum.

1, 1, 1, 3, 8, 24, 74, 238, 786, 2646, 9071, 31536, 110967, 394420, 1414053, 5107523, 18568628, 67894564, 249513890, 921134164, 3414439996, 12703212213, 47419589969, 177551521838, 666655929561, 2509526456940, 9469082269965, 35807434636137, 135681047696427

Offset: 0

Author

Alois P. Heinz, Jan 31 2017

Keywords

• nonn

Examples

			a(0) = 1: {}.
a(1) = 1: {1}.
a(2) = 1: {1,3}.
a(3) = 3: {1,2,6}, {1,3,5}, {2,3,4}.
a(4) = 8: {1,2,5,8}, {1,2,6,7}, {1,3,4,8}, {1,3,5,7}, {1,4,5,6}, {2,3,4,7}, {2,3,5,6}, {4,6,7,8}.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..130

Crossrefs

Cf. A281871, A284251.

Formula

a(n) = A281871(2n,n).