A069690 Primes that yield another prime on placing a 9 on both sides (as leading and trailing digits).

2, 19, 23, 31, 41, 43, 47, 53, 61, 67, 71, 73, 83, 101, 107, 109, 113, 149, 163, 193, 211, 239, 241, 263, 269, 277, 313, 317, 331, 347, 373, 397, 409, 421, 439, 443, 499, 521, 523, 541, 547, 607, 617, 619, 641, 647, 673, 677, 757, 787, 829, 863, 877, 907, 911

Offset: 1

Author

Amarnath Murthy, Apr 06 2002

Keywords

• nonn
• base

Examples

			241 belongs to this sequence as 92419 is also a prime.
		

Links

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

Crossrefs

Cf. A069687, A069688, A069689.

Programs

Maple

filter:= proc(n) isprime(9+10*n+9*10^(2+ilog10(n))) end proc:
select(filter, [seq(ithprime(i),i=1..1000)]); # Robert Israel, Feb 02 2021

Mathematica

Select[ Range[2000], PrimeQ[ # ] && PrimeQ[ FromDigits[ Insert[ IntegerDigits[ # ], 9, {{1}, {-1}}]]] &]
Select[Prime[Range[200]],PrimeQ[FromDigits[Join[{9},IntegerDigits[#],{9}]]]&] (* Harvey P. Dale, Nov 07 2022 *)

Python

from sympy import isprime, primerange
def ok(p): return isprime(int('9'+str(p)+'9'))
def aupto(lim): return [p for p in primerange(2, lim+1) if ok(p)]
print(aupto(911)) # Michael S. Branicky, Feb 19 2021

Extensions

Edited and extended by Robert G. Wilson v, May 03 2002