cp's OEIS Frontend

A115688 Semiprimes (A001358) whose digit reversal is a powerful(1) number (A001694).

%I A115688 #5 Dec 03 2019 21:13:16
%S A115688 4,9,10,46,94,121,169,215,526,869,961,982,1042,1273,1405,1843,2918,
%T A115688 3194,4069,4633,5213,5221,5758,6313,6511,6937,8045,8402,8651,8882,
%U A115688 9235,9481,9586,9886,10201,10609,12538,12769,14023,16171,16327,16582
%N A115688 Semiprimes (A001358) whose digit reversal is a powerful(1) number (A001694).
%H A115688 Robert Israel, <a href="/A115688/b115688.txt">Table of n, a(n) for n = 1..908</a>
%e A115688 869=11*79 is semiprime and 968=2^3*11^2 is powerful.
%p A115688 N:= 99999:
%p A115688 S:= {1}:
%p A115688 p:= 1:
%p A115688 do
%p A115688   p:= nextprime(p);
%p A115688   if p^2 > N then break fi;
%p A115688   S:= S union map(t -> seq(t*p^j,j=2..floor(log[p](N/t))), S);
%p A115688 od:
%p A115688 digrev:= proc(x) local L;
%p A115688   L:= convert(x,base,10);
%p A115688   add(L[-i]*10^(i-1),i=1..nops(L))
%p A115688 end proc:
%p A115688 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
%Y A115688 Cf. A001358, A001694, A115687.
%K A115688 nonn,base
%O A115688 1,1
%A A115688 _Giovanni Resta_, Jan 31 2006