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
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
Programs
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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
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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
Comments