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

1,1

Links

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

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A069687, A069688, A069689.

Sequence in context: A019348 A155025 A191068 * A037003 A105907 A018696

Adjacent sequences: A069687 A069688 A069689 * A069691 A069692 A069693

Keyword

nonn,base

Author

Amarnath Murthy, Apr 06 2002

Extensions

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

Status

approved