A064507 - OEIS

%I #16 Dec 04 2016 03:57:46

%S 21,27,29,61,67,111,151,191,201,203,223,241,313,319,331,351,373,397,

%T 403,409,461,463,481,553,559,571,667,711,791,807,841,869,889,931,979,

%U 1071,1079,1107,1129,1189,1257,1273,1277,1297,1431,1437,1583,1611,1639

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

%C All terms are coprime to 10. - _Robert Israel_, Dec 04 2016

%H Robert Israel, <a href="/A064507/b064507.txt">Table of n, a(n) for n = 1..10000</a>

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

%p filter:= proc(n) local L,i;

%p    L:= convert(n,base, 10);

%p    isprime(add(L[i]*n^(i-1),i=1..nops(L)))

%p end proc:

%p select(filter, [seq(i,i=11..2000,2)]); # _Robert Israel_, Dec 04 2016

%o (PARI) isok(n) = (n>=10) && isprime(fromdigits(digits(n), n)); \\ _Michel Marcus_, Dec 04 2016

%Y Cf. A064508.  Contained in A054684.

%K nonn,base

%O 1,1

%A _Jon Perry_, Oct 06 2001

%E Offset corrected by _Arkadiusz Wesolowski_, Oct 19 2013

%E Name corrected by _Robert Israel_, Dec 04 2016