A262210 Numbers whose decimal digits are the concatenation of a nonprime followed by a prime.

12, 13, 15, 17, 43, 45, 47, 67, 83, 93, 95, 97, 103, 107, 113, 123, 125, 127, 129, 131, 137, 141, 143, 147, 153, 157, 159, 161, 163, 165, 167, 171, 173, 179, 183, 185, 187, 193, 197, 402, 403, 405, 407, 411, 413, 417, 419, 423, 429, 431, 437, 441, 443, 447, 453, 459, 461, 467, 471

Offset: 1

Author

Giovanni Teofilatto, Sep 15 2015

Keywords

• nonn
• base

Crossrefs

Cf. A125664.

Programs

PARI

is(n)=if(gcd(n,10)>1,return(!isprime(n\10) && n>9 && isprime(n%10))); for(k=1,#Str(n)-1, if(isprime(n%10^k) && !isprime(n\10^k), return(1))); 0 \\ Charles R Greathouse IV, Sep 15 2015