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

1,1

Comments

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

Links

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

Example

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.

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);

Prog

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

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).

Sequence in context: A112681 A078500 A155913 * A240898 A244077 A277206

Adjacent sequences: A227916 A227917 A227918 * A227920 A227921 A227922

Keyword

nonn,base

Author

K. D. Bajpai, Oct 10 2013

Status

approved