Triangular numbers (A000217) whose second arithmetic derivative (A068346) is also a triangular number.

A351131

Triangular numbers (A000217) whose second arithmetic derivative (A068346) is also a triangular number.

Terms

    a(0) =0a(1) =1a(2) =3a(3) =6a(4) =10a(5) =66a(6) =78a(7) =105a(8) =231a(9) =325a(10) =465a(11) =561a(12) =595a(13) =861a(14) =1378a(15) =2211a(16) =2278a(17) =2485a(18) =3081a(19) =3570a(20) =3655a(21) =4278a(22) =4465a(23) =5253a(24) =6441a(25) =6670a(26) =8515a(27) =8778a(28) =9453a(29) =9870

External references