Triangular numbers (A000217) with indices A000043.

Terms

a(0) =3a(1) =6a(2) =15a(3) =28a(4) =91a(5) =153a(6) =190a(7) =496a(8) =1891a(9) =4005a(10) =5778a(11) =8128a(12) =135981a(13) =184528a(14) =818560a(15) =2427706a(16) =2602621a(17) =5176153a(18) =9046131a(19) =9783676a(20) =46943205a(21) =49416711a(22) =62871291a(23) =198751953a(24) =235477551a(25) =269340445a(26) =990013753a(27) =3718970646a(28) =6105511756a(29) =8718535225