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

1,1

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).

Mathematica

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

Prog

(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

Crossrefs

Cf. A077359, A077360.

Sequence in context: A080540 A334105 A077358 * A077360 A102636 A335314

Adjacent sequences: A069683 A069684 A069685 * A069687 A069688 A069689

Keyword

base,nonn,easy

Author

Amarnath Murthy, Nov 05 2002

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

Status

approved