A023107 Largest integer in which every prefix is prime in base n (written in base 10).

71, 191, 2437, 108863, 6841, 4497359, 1355840309, 73939133, 6774006887, 18704078369, 122311273757, 6525460043032393259, 927920056668659, 16778492037124607, 4928397730238375565449, 5228233855704101657, 3013357583408354653, 1437849529085279949589, 101721177350595997080671, 185720479816277907890970001

Offset: 3

Author

David W. Wilson

Keywords

• nonn
• base

Comments

Or, largest right-truncatable prime with base n>2 (in decimal form).

a(n) <= A094335(n).

Examples

			a(100) = 70123916363515199416199518301698321195339012727994799// 190371992151279729974757397909992327936943877127375781091143. - _Giovanni Resta_, Apr 11 2016
		

Links

• Martin Renner, Max Alekseyev and Giovanni Resta, Table of n, a(n) for n = 3..100
• I. O. Angell and H. J. Godwin, On Truncatable Primes, Math. Comput. 31, 265-267, 1977.
• N. J. A. Sloane, The Angell-Godwin table of initial terms of A023107 and A103443
• Eric Weisstein's World of Mathematics, Truncatable Prime.
• Index entries for sequences related to truncatable primes

Crossrefs

Cf. A076586.

Programs

PARI

a(n) = my(S,m,D); D=select(x->(gcd(x,n)==1),vector(n-1,j,j)); S=select(ispseudoprime,vector(n-1,i,i)); while(#S, m=vecmax(S); S=concat(vector(#D,j,select(ispseudoprime,vector(#S,i,S[i]*n+D[j]))));); m /* Max Alekseyev, Dec 09 2014 */

Extensions

More terms from Don Reble, Jun 23 2004

a(54)-a(75) in b-file from Max Alekseyev, Dec 09 2014

a(76)-a(100) in b-file from Giovanni Resta, May 01 2016