A102173 Iccanobirt semiprime indices (3 of 15): Indices of semiprime numbers in A102113.

5, 9, 11, 16, 22, 29, 67, 72, 87, 90, 94, 95, 119, 123, 146, 188, 323, 330

Offset: 1

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

• nonn
• more
• less
• base

Crossrefs

Cf. A001358, A102113, A102171-A102185, A102193.

Programs

Mathematica

nxt[{a1_,a2_,a3_}]:={a2,a3,a3+FromDigits[Reverse[IntegerDigits[a1]]]+ FromDigits[Reverse[IntegerDigits[a2]]]}; Flatten[Position[Transpose[ NestList[nxt,{0,0,1},200]][[1]],?(PrimeOmega[#]==2&)]]-1 (* _Harvey P. Dale, Oct 17 2012 *)

Formula

A102113(a(n)) = A102193(n).

Extensions

Offset changed to 1 and a(17)-a(18) from Jinyuan Wang, Aug 10 2021