A210616 Digit reversal of n-th semiprime.

4, 6, 9, 1, 41, 51, 12, 22, 52, 62, 33, 43, 53, 83, 93, 64, 94, 15, 55, 75, 85, 26, 56, 96, 47, 77, 28, 58, 68, 78, 19, 39, 49, 59, 601, 111, 511, 811, 911, 121, 221, 321, 921, 331, 431, 141, 241, 341, 541, 641, 551, 851, 951, 161, 661, 961, 771, 871, 381

Offset: 1

Author

Jonathan Vos Post, Mar 23 2012

Keywords

• nonn
• base
• easy

Comments

The fixed points where a(n) = n are A046328.

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..2000

Crossrefs

Cf. A001358, A004086, A046328.

Programs

Mathematica

t = Select[Range[200], PrimeOmega[#] == 2 &]; FromDigits[Reverse[IntegerDigits[#]]] & /@ t (* T. D. Noe, Mar 26 2012 *)
IntegerReverse/@Select[Range[500],PrimeOmega[#]==2&] (* Harvey P. Dale, Dec 06 2021 *)

Formula

a(n) = R(A001358(n)) = A004086(A001358(n)).