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

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

Offset: 1

Author

Giovanni Resta, Jan 31 2006

Keywords

• nonn
• base

Examples

			869=11*79 is semiprime and 968=2^3*11^2 is powerful.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..908

Crossrefs

Cf. A001358, A001694, A115687.

Programs

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