rumus suku ke-n dari. 1,6,14,27,49,86

1,6,14,27,49,86...
↓ selisih
5,8,13,22,37,...
↓ selisih
3,5,9,15,...
↓ selisih
2,4,6,...
↓ selisih
2,2...
↓ selisih
0 (berhenti)

a = 1
b = 5
c = 3
d = 2
e = 2

Un = a/0! + b(n-1)/1! + c(n-1)(n-2)/2! + d(n-1)(n-2)(n-3)/3! + d(n-1)(n-2)(n-3)(n-4)/4! + e(n-1)(n-2)(n-3)(n-4)(n-5)/5!
Un = 1 + 5(n-1) + 3/2(n-1)(n-2) + ⅓(n-1)(n-2)(n-3) + 1/12(n-1)(n-2)(n-3)(n-4) + 1/60(n-1)(n-2)(n-3)(n-4)(n-5)