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

1,1

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

Table of n, a(n) for n=1..31.

Lucas A. Brown, A101766.py.

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 *)

Crossrefs

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

Sequence in context: A180860 A356450 A328189 * A338930 A357002 A356441

Adjacent sequences: A101763 A101764 A101765 * A101767 A101768 A101769

Keyword

nonn,base,hard,more

Author

Jonathan Vos Post and Ray Chandler, Dec 15 2004

Extensions

Offset changed to 1 by Jinyuan Wang, Aug 01 2021

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

Status

approved