Convolution of A008805 (triangular numbers repeated) with itself.

Terms

a(0) =1a(1) =2a(2) =7a(3) =12a(4) =27a(5) =42a(6) =77a(7) =112a(8) =182a(9) =252a(10) =378a(11) =504a(12) =714a(13) =924a(14) =1254a(15) =1584a(16) =2079a(17) =2574a(18) =3289a(19) =4004a(20) =5005a(21) =6006a(22) =7371a(23) =8736a(24) =10556a(25) =12376a(26) =14756a(27) =17136a(28) =20196a(29) =23256