A114019 Largest n-digit prime whose digit reversal is also prime.

7, 97, 991, 9967, 99989, 999983, 9999971, 99999827, 999999893, 9999999967, 99999999977, 999999999959, 9999999999799, 99999999999959, 999999999999877, 9999999999999571, 99999999999997997, 999999999999999737, 9999999999999999719, 99999999999999999631

Offset

1,1

Links

Michael S. Branicky, Table of n, a(n) for n = 1..527

Mathematica

f[n_] := Block[{k = 10^n}, While[ !PrimeQ[k] || !PrimeQ[FromDigits@Reverse@IntegerDigits@k], k-- ]; k]; Array[f, 19] (* Robert G. Wilson v, Nov 19 2005 *)

Prog

(Python)
from sympy import isprime
def c(n): return isprime(n) and isprime(int(str(n)[::-1]))
def a(n): return next(p for p in range(10**n-1, 10**(n-1), -2) if c(p))
print([a(n) for n in range(1, 21)]) # Michael S. Branicky, Jun 27 2022

Crossrefs

Cf. A113018.

Sequence in context: A071361 A007810 A146758 * A178007 A241206 A127892

Adjacent sequences: A114016 A114017 A114018 * A114020 A114021 A114022

Keyword

base,nonn

Author

Amarnath Murthy, Nov 12 2005

Extensions

More terms from Robert G. Wilson v, Nov 19 2005

a(19) and beyond from Michael S. Branicky, Jun 27 2022

Status

approved