A046394 Palindromes with exactly 4 distinct prime factors.

858, 2002, 2442, 3003, 4774, 5005, 5115, 6666, 10101, 15351, 17871, 22422, 22722, 24242, 26562, 26962, 28482, 35853, 36363, 41314, 43734, 43834, 45654, 47874, 49494, 49794, 49894, 51015, 51315, 51415, 53535, 53835, 53935, 56865, 58485

Offset: 1

Author

Patrick De Geest, Jun 15 1998

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A046330, A046410.

Programs

Maple

filter:= proc(n) local F;
  F:= ifactors(n)[2];
  nops(F)=4 and max(map(t->t[2],F))=1
end proc:
makepali:= proc(n,d) local L;
  L:= convert(n,base,10);
  if d::even then 10^(d/2)*n + add(L[i]*10^(d/2-i),i=1..d/2)
  else 10^((d-1)/2)*n + add(L[i]*10^((d+1)/2-i),i=2..(d+1)/2)
  fi
end proc:
select(filter, [seq(seq(makepali(x,d),
   x=10^ceil(d/2-1)..10^ceil(d/2)-1),d=1..6)]); # Robert Israel, Jun 05 2018

Mathematica

Select[Range[60000],PalindromeQ[#]&&PrimeNu[#]==Total[FactorInteger[#][[All,2]]] == 4&] (* Harvey P. Dale, Apr 07 2022 *)