cp's OEIS Frontend

A046375 Odd numbers with exactly 5 palindromic prime factors (counted with multiplicity).

%I A046375 #12 Mar 15 2024 07:26:57
%S A046375 243,405,567,675,891,945,1125,1323,1485,1575,1875,2079,2205,2475,2625,
%T A046375 3087,3125,3267,3465,3675,4125,4375,4851,5145,5445,5775,6125,6875,
%U A046375 7203,7623,8085,8181,8575,9075,9625,10611,11319,11979,12005,12231,12705
%N A046375 Odd numbers with exactly 5 palindromic prime factors (counted with multiplicity).
%H A046375 Robert Israel, <a href="/A046375/b046375.txt">Table of n, a(n) for n = 1..10000</a>
%p A046375 rev:= proc(n) local L,d,i;
%p A046375   L:= convert(n,base,10);
%p A046375   d:= nops(L);
%p A046375   add(L[i]*10^(d-i),i=1..d);
%p A046375 end proc:
%p A046375 PP:= NULL:
%p A046375 for d from 1 to 3 do
%p A046375   for x from 10^(d-1) to 10^d-1 do
%p A046375     y:= x*10^(d-1) + rev(floor(x/10));
%p A046375     if isprime(y) then PP:= PP,y fi;
%p A046375   od;
%p A046375   if d = 1 then PP:= PP,11 fi;
%p A046375 od:
%p A046375 PP:= [PP][2..-1]:
%p A046375 npp:= nops(PP):
%p A046375 N:= PP[-1]*3^4:
%p A046375 Res:= NULL:
%p A046375 for i1 from 1 to npp do
%p A046375      v1:= PP[i1];
%p A046375      for i2 from 1 to i1 do
%p A046375        v2:= v1*PP[i2];
%p A046375        if v2*3^3 > N then break fi;
%p A046375        for i3 from 1 to i2 do
%p A046375          v3:= v2*PP[i3];
%p A046375          if v3 * 3^2 > N then break fi;
%p A046375          for i4 from 1 to i3 do
%p A046375            v4:= v3*PP[i4];
%p A046375            if v4* 3 > N then break fi;
%p A046375            for i5 from 1 to i4 do
%p A046375              v:= v4*PP[i5];
%p A046375              if v > N then break fi;
%p A046375              Res:= Res, v
%p A046375 od od od od od:
%p A046375 sort([Res]); # _Robert Israel_, Mar 15 2024
%Y A046375 Cf. A046318, A046407.
%K A046375 nonn,base
%O A046375 1,1
%A A046375 _Patrick De Geest_, Jun 15 1998
%E A046375 Offset corrected by _Robert Israel_, Mar 15 2024