Number of 4-element subsets of [n] whose sum is a triangular number.

Terms

a(0) =1a(1) =1a(2) =3a(3) =6a(4) =11a(5) =20a(6) =32a(7) =48a(8) =70a(9) =98a(10) =132a(11) =174a(12) =226a(13) =287a(14) =359a(15) =444a(16) =542a(17) =655a(18) =783a(19) =928a(20) =1092a(21) =1275a(22) =1479a(23) =1707a(24) =1957a(25) =2231a(26) =2534a(27) =2865a(28) =3225a(29) =3617