A069686 Primes whose internal digits form a prime.

127, 131, 137, 139, 151, 157, 173, 179, 223, 227, 229, 233, 239, 251, 257, 271, 277, 331, 337, 353, 359, 373, 379, 421, 431, 433, 439, 457, 479, 521, 523, 557, 571, 577, 631, 653, 659, 673, 677, 727, 733, 739, 751, 757, 773, 821, 823, 827, 829, 839, 853

Offset: 1

Author

Amarnath Murthy, Nov 05 2002

Keywords

• base
• nonn
• easy

Comments

Primes that remain prime upon deleting the first and last digits.

Links

• Jason Yuen, Table of n, a(n) for n = 1..10000 (correcting Christian N. K. Anderson previous bfile).

Crossrefs

Cf. A077359, A077360.

Programs

Mathematica

Select[Range[100, 853], PrimeQ[#] && PrimeQ[FromDigits[Rest[Most[IntegerDigits[#]]]]] &] (* T. D. Noe, Apr 05 2013 *)

PARI

{indigs(n)=local(j,a,d); n=n\10; j=1; a=0; while(n>10,d=divrem(n,10); n=d[1]; a=a+j*d[2]; j=10*j); a}
forprime(p=1,855,if(isprime(indigs(p)),print1(p,","))) \\ Klaus Brockhaus, Nov 06 2002

Python

from sympy import isprime
for p in filter(isprime, range(100, 855)):
    if isprime(int(str(p)[1:-1])): print(p) # Jason Yuen, Mar 28 2024

Extensions

Edited and extended by Klaus Brockhaus, Nov 06 2002

Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 21 2007