A064507 Numbers of more than one digit that yield primes when cast in their own base.

21, 27, 29, 61, 67, 111, 151, 191, 201, 203, 223, 241, 313, 319, 331, 351, 373, 397, 403, 409, 461, 463, 481, 553, 559, 571, 667, 711, 791, 807, 841, 869, 889, 931, 979, 1071, 1079, 1107, 1129, 1189, 1257, 1273, 1277, 1297, 1431, 1437, 1583, 1611, 1639

Offset: 1

Author

Jon Perry, Oct 06 2001

Keywords

• nonn
• base

Comments

All terms are coprime to 10. - Robert Israel, Dec 04 2016

Examples

			E.g. 21 in base 21 is 2*21+1=43, 111 is 1*111*111+1*111+1=12433, etc.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A064508. Contained in A054684.

Programs

Maple

filter:= proc(n) local L,i;
   L:= convert(n,base, 10);
   isprime(add(L[i]*n^(i-1),i=1..nops(L)))
end proc:
select(filter, [seq(i,i=11..2000,2)]); # Robert Israel, Dec 04 2016

PARI

isok(n) = (n>=10) && isprime(fromdigits(digits(n), n)); \\ Michel Marcus, Dec 04 2016

Extensions

Offset corrected by Arkadiusz Wesolowski, Oct 19 2013

Name corrected by Robert Israel, Dec 04 2016