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A046394 Palindromes with exactly 4 distinct prime factors.

%I A046394 #16 Apr 07 2022 16:30:07
%S A046394 858,2002,2442,3003,4774,5005,5115,6666,10101,15351,17871,22422,22722,
%T A046394 24242,26562,26962,28482,35853,36363,41314,43734,43834,45654,47874,
%U A046394 49494,49794,49894,51015,51315,51415,53535,53835,53935,56865,58485
%N A046394 Palindromes with exactly 4 distinct prime factors.
%H A046394 Robert Israel, <a href="/A046394/b046394.txt">Table of n, a(n) for n = 1..10000</a>
%p A046394 filter:= proc(n) local F;
%p A046394   F:= ifactors(n)[2];
%p A046394   nops(F)=4 and max(map(t->t[2],F))=1
%p A046394 end proc:
%p A046394 makepali:= proc(n,d) local L;
%p A046394   L:= convert(n,base,10);
%p A046394   if d::even then 10^(d/2)*n + add(L[i]*10^(d/2-i),i=1..d/2)
%p A046394   else 10^((d-1)/2)*n + add(L[i]*10^((d+1)/2-i),i=2..(d+1)/2)
%p A046394   fi
%p A046394 end proc:
%p A046394 select(filter, [seq(seq(makepali(x,d),
%p A046394    x=10^ceil(d/2-1)..10^ceil(d/2)-1),d=1..6)]); # _Robert Israel_, Jun 05 2018
%t A046394 Select[Range[60000],PalindromeQ[#]&&PrimeNu[#]==Total[FactorInteger[#][[All,2]]] == 4&] (* _Harvey P. Dale_, Apr 07 2022 *)
%Y A046394 Cf. A046330, A046410.
%K A046394 nonn,base
%O A046394 1,1
%A A046394 _Patrick De Geest_, Jun 15 1998