A227919 Primes which remain prime when rightmost digit is removed.

23, 29, 31, 37, 53, 59, 71, 73, 79, 113, 131, 137, 139, 173, 179, 191, 193, 197, 199, 233, 239, 293, 311, 313, 317, 373, 379, 419, 431, 433, 439, 479, 593, 599, 613, 617, 619, 673, 677, 719, 733, 739, 797, 839, 971, 977, 1013, 1019, 1031, 1033, 1039, 1091, 1093

Offset: 1

Author

K. D. Bajpai, Oct 10 2013

Keywords

• nonn
• base

Comments

After a(2), all the terms in this sequence have second digit from right 1, 3, 7, or 9.

Examples

			a(7)= 71 which is prime. Removing the rightmost digit gives 7, which is also prime.
a(16)= 191 which is prime. Removing the rightmost digit gives 19, which is also prime.
		

Links

• K. D. Bajpai, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040 (prime numbers), A024770 (right-truncatable primes).

Cf. A052025 (palindromic prime is prime right- or left-truncatable).

Cf. A137812 (left- or right-truncatable primes).

Programs

Maple

KD:= proc() local a,b; a:= ithprime(n); b:=floor(a/10); if isprime(b) then return (a) :fi; end: seq(KD(),n=1..1000);

PARI

is(n)=isprime(n) && isprime(n\10) \\ Charles R Greathouse IV, Oct 12 2013