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A046394
Palindromes with exactly 4 distinct prime factors.
3
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
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
Sequence in context: A087002 A256743 A307330 * A163304 A252237 A284074
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Jun 15 1998
STATUS
approved