A240768 Left-truncatable primes p with property that prepending any single decimal digit to p does not produce a prime.
2, 5, 773, 3373, 3947, 4643, 5113, 6397, 6967, 7937, 15647, 16823, 24373, 33547, 34337, 37643, 56983, 57853, 59743, 62383, 63347, 63617, 69337, 72467, 72617, 75653, 76367, 87643, 92683, 97883, 98317, 121997, 124337, 163853, 213613, 236653, 242467, 242797
Offset: 1
Examples
3373 belongs to this sequence because 3373, 373, 73 and 3 are all prime; k*10^4 + 3373, for k = 1 to 9, are all composite.
Links
- Chris Caldwell, The Prime Glossary, Left-truncatable prime
- Eric Weisstein's World of Mathematics, Truncatable Prime
- Index entries for sequences related to truncatable primes
Programs
-
PARI
for(n=2, 242797, v=n; while(isprime(n), c=n; n=lift(Mod(c, 10^(#Str(c)-1))); if(!(#Str(c)-#Str(n)==1), break)); if(n==0, s=#Str(v); t=0; for(k=1, 9, if(isprime(k*10^s+v), break, t++)); if(t==9, print1(v, ", "))); n=v);