The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A115688 Semiprimes (A001358) whose digit reversal is a powerful(1) number (A001694). 2
 4, 9, 10, 46, 94, 121, 169, 215, 526, 869, 961, 982, 1042, 1273, 1405, 1843, 2918, 3194, 4069, 4633, 5213, 5221, 5758, 6313, 6511, 6937, 8045, 8402, 8651, 8882, 9235, 9481, 9586, 9886, 10201, 10609, 12538, 12769, 14023, 16171, 16327, 16582 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..908 EXAMPLE 869=11*79 is semiprime and 968=2^3*11^2 is powerful. MAPLE N:= 99999: S:= {1}: p:= 1: do p:= nextprime(p); if p^2 > N then break fi; S:= S union map(t -> seq(t*p^j, j=2..floor(log[p](N/t))), S); od: digrev:= proc(x) local L; L:= convert(x, base, 10); add(L[-i]*10^(i-1), i=1..nops(L)) end proc: sort(convert({10} union select(t -> numtheory:-bigomega(t)=2, map(digrev, select(t -> t mod 10 <> 0, S))), list)); # Robert Israel, Dec 03 2019 CROSSREFS Cf. A001358, A001694, A115687. Sequence in context: A178360 A197125 A197129 * A115710 A082749 A220427 Adjacent sequences: A115685 A115686 A115687 * A115689 A115690 A115691 KEYWORD nonn,base AUTHOR Giovanni Resta, Jan 31 2006 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 31 12:46 EDT 2023. Contains 363066 sequences. (Running on oeis4.)