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

0,4

Links

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

Formula

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

Example

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}.

Crossrefs

Cf. A281871, A284251.

Sequence in context: A291886 A275856 A303607 * A046342 A238977 A182453

Adjacent sequences: A281869 A281870 A281871 * A281873 A281874 A281875

Keyword

nonn

Author

Alois P. Heinz, Jan 31 2017

Status

approved