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

1,1

Links

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

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

Crossrefs

Cf. A046318, A046407.

Sequence in context: A362584 A223021 A046318 * A226064 A157958 A232924

Adjacent sequences: A046372 A046373 A046374 * A046376 A046377 A046378

Keyword

nonn,base

Author

Patrick De Geest, Jun 15 1998

Extensions

Offset corrected by Robert Israel, Mar 15 2024

Status

approved