Indices of triangular numbers that are ten times other triangular numbers.

Terms

a(0) =0a(1) =4a(2) =20a(3) =39a(4) =175a(5) =779a(6) =1500a(7) =6664a(8) =29600a(9) =56979a(10) =253075a(11) =1124039a(12) =2163720a(13) =9610204a(14) =42683900a(15) =82164399a(16) =364934695a(17) =1620864179a(18) =3120083460a(19) =13857908224a(20) =61550154920a(21) =118481007099a(22) =526235577835