A101766 Iccanobif semiprime indices: Indices of semiprime numbers in A014260.

8, 16, 18, 21, 26, 38, 42, 44, 49, 54, 55, 57, 61, 67, 77, 78, 115, 123, 134, 145, 151, 154, 202, 218, 249, 286, 349, 403, 498, 539, 647

Offset: 1

Author

Jonathan Vos Post and Ray Chandler, Dec 15 2004

Keywords

• nonn
• base
• hard
• more

Comments

This sequence also includes 790, 1161, 1347, 1418, 1595, 1761, and 2018. It might or might not include 769, 1394, 1795, 1983, 2093, 2178, but the required factoring proved rather difficult. There are no further terms below 2178. - Lucas A. Brown, Nov 12 2022

Links

• Lucas A. Brown, A101766.py.

Crossrefs

Cf. A001358, A001129, A014258, A014259, A014260, A101763, A101764, A101765.

Programs

Mathematica

nxt[{a_,b_}]:={b,IntegerReverse[a]+b}; Flatten[Position[NestList[nxt,{0,1},600][[All,1]],?(PrimeOmega[#]==2&)]]-1 (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale, Jul 04 2018 *)

Extensions

Offset changed to 1 by Jinyuan Wang, Aug 01 2021

a(31) from Lucas A. Brown, Nov 12 2022