Index of 8^n within the sequence of the numbers of the form 7^i*8^j.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =15a(5) =21a(6) =28a(7) =36a(8) =45a(9) =55a(10) =66a(11) =78a(12) =91a(13) =105a(14) =120a(15) =137a(16) =155a(17) =174a(18) =194a(19) =215a(20) =237a(21) =260a(22) =284a(23) =309a(24) =335a(25) =362a(26) =390a(27) =419a(28) =449a(29) =480