A076055 Composite numbers which when read backwards are primes.

14, 16, 20, 30, 32, 34, 35, 38, 50, 70, 74, 76, 91, 92, 95, 98, 104, 106, 110, 112, 118, 119, 124, 125, 128, 130, 133, 134, 136, 140, 142, 145, 146, 152, 160, 164, 166, 170, 172, 175, 182, 188, 194, 196, 200, 300, 301, 305, 310, 316, 320, 322, 325, 328, 332

Offset: 1

Author

Amarnath Murthy, Oct 04 2002

Keywords

• base
• nonn

Comments

If m is a term, then 10*m is another term. - Bernard Schott, Nov 20 2021

Links

• Michael S. Branicky, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A076056.

Intersection of A002808 and A095179.

Programs

Mathematica

Rev[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Select[Range[332],!PrimeQ[#] && PrimeQ[Rev[#]]&] (* Jayanta Basu, May 01 2013 *)

Python

from sympy import isprime
def ok(n): return not isprime(n) and isprime(int(str(n)[::-1]))
print([k for k in range(333) if ok(k)]) # Michael S. Branicky, Nov 20 2021

Extensions

Corrected and extended by Sascha Kurz, Jan 20 2003