a(n) = position of n^2 + (n+1)^2 + (n+2)^2 in A000408.

Terms

a(0) =6a(1) =15a(2) =30a(3) =50a(4) =75a(5) =104a(6) =140a(7) =181a(8) =228a(9) =279a(10) =335a(11) =396a(12) =463a(13) =533a(14) =610a(15) =693a(16) =779a(17) =870a(18) =968a(19) =1070a(20) =1177a(21) =1289a(22) =1405a(23) =1528a(24) =1655a(25) =1785a(26) =1923a(27) =2064a(28) =2211a(29) =2364