Doubly octagonal pyramidal numbers.

Terms

a(0) =0a(1) =1a(2) =765a(3) =27435a(4) =345415a(5) =2469420a(6) =12352956a(7) =48294610a(8) =157609530a(9) =447989355a(10) =1141711615a(11) =2663460261a(12) =5775482505a(13) =11777133550a(14) =22789550070a(15) =42150245460a(16) =74946834916a(17) =128723876325a(18) =214401953745a(19) =347453633935a(20) =549386792955a(21) =849592039296