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

1,1

Links

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

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 *)

Crossrefs

Cf. A046330, A046410.

Sequence in context: A087002 A256743 A307330 * A163304 A252237 A284074

Adjacent sequences: A046391 A046392 A046393 * A046395 A046396 A046397

Keyword

nonn,base

Author

Patrick De Geest, Jun 15 1998

Status

approved