A366430 Triprimes whose reversal is also a triprime.

8, 44, 66, 99, 117, 147, 165, 171, 212, 222, 242, 244, 246, 282, 285, 286, 290, 292, 333, 338, 343, 363, 366, 369, 404, 406, 418, 425, 434, 435, 438, 442, 474, 475, 494, 498, 506, 507, 508, 524, 534, 539, 548, 555, 561, 574, 575, 582, 595, 604, 605, 606, 609, 628, 642, 646, 663, 670, 682, 705

Offset: 1

Author

Zak Seidov and Robert Israel, Nov 06 2023

Keywords

• nonn
• base

Examples

			a(5) = 117 is a term because 117 = 3^2 * 13 has 3 prime factors, counted with multiplicity, and so does its reversal 711 = 3^2 * 79.
		

Links

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

Crossrefs

Cf. A014612, A085751. Contains A046329. Includes 10*k for k in A367151.

Programs

Maple

rev:= proc(n) local L,i;
  L:= convert(n,base,10);
  add(L[-i]*10^(i-1),i=1..nops(L))
end proc:
select(t -> numtheory:-bigomega(t) = 3 and numtheory:-bigomega(rev(t))=3, [$1..10000]);

Mathematica

Select[Range[710], PrimeOmega[#]==3&&PrimeOmega[FromDigits[Reverse[IntegerDigits[#]]]]==3&] (* Stefano Spezia, Nov 07 2023 *)

Python

from sympy import factorint
def tp(n): return sum(factorint(n).values()) == 3
def ok(n): return tp(n) and tp(int(str(n)[::-1]))
print([k for k in range(10**3) if ok(k)]) # Michael S. Branicky, Nov 21 2023