Index of 10^n within the sequence of the numbers of the form 7^i*10^j.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =15a(5) =21a(6) =29a(7) =38a(8) =48a(9) =59a(10) =71a(11) =85a(12) =100a(13) =116a(14) =133a(15) =151a(16) =170a(17) =191a(18) =213a(19) =236a(20) =260a(21) =285a(22) =312a(23) =340a(24) =369a(25) =399a(26) =430a(27) =462a(28) =496a(29) =531