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

243, 405, 567, 675, 891, 945, 1125, 1323, 1485, 1575, 1875, 2079, 2205, 2475, 2625, 3087, 3125, 3267, 3465, 3675, 4125, 4375, 4851, 5145, 5445, 5775, 6125, 6875, 7203, 7623, 8085, 8181, 8575, 9075, 9625, 10611, 11319, 11979, 12005, 12231, 12705

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. A046318, A046407.

Programs

Maple

rev:= proc(n) local L,d,i;
  L:= convert(n,base,10);
  d:= nops(L);
  add(L[i]*10^(d-i),i=1..d);
end proc:
PP:= NULL:
for d from 1 to 3 do
  for x from 10^(d-1) to 10^d-1 do
    y:= x*10^(d-1) + rev(floor(x/10));
    if isprime(y) then PP:= PP,y fi;
  od;
  if d = 1 then PP:= PP,11 fi;
od:
PP:= [PP][2..-1]:
npp:= nops(PP):
N:= PP[-1]*3^4:
Res:= NULL:
for i1 from 1 to npp do
     v1:= PP[i1];
     for i2 from 1 to i1 do
       v2:= v1*PP[i2];
       if v2*3^3 > N then break fi;
       for i3 from 1 to i2 do
         v3:= v2*PP[i3];
         if v3 * 3^2 > N then break fi;
         for i4 from 1 to i3 do
           v4:= v3*PP[i4];
           if v4* 3 > N then break fi;
           for i5 from 1 to i4 do
             v:= v4*PP[i5];
             if v > N then break fi;
             Res:= Res, v
od od od od od:
sort([Res]); # Robert Israel, Mar 15 2024

Extensions

Offset corrected by Robert Israel, Mar 15 2024