cp's OEIS Frontend

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

%I A064507 #16 Dec 04 2016 03:57:46
%S A064507 21,27,29,61,67,111,151,191,201,203,223,241,313,319,331,351,373,397,
%T A064507 403,409,461,463,481,553,559,571,667,711,791,807,841,869,889,931,979,
%U A064507 1071,1079,1107,1129,1189,1257,1273,1277,1297,1431,1437,1583,1611,1639
%N A064507 Numbers of more than one digit that yield primes when cast in their own base.
%C A064507 All terms are coprime to 10. - _Robert Israel_, Dec 04 2016
%H A064507 Robert Israel, <a href="/A064507/b064507.txt">Table of n, a(n) for n = 1..10000</a>
%e A064507 E.g. 21 in base 21 is 2*21+1=43, 111 is 1*111*111+1*111+1=12433, etc.
%p A064507 filter:= proc(n) local L,i;
%p A064507    L:= convert(n,base, 10);
%p A064507    isprime(add(L[i]*n^(i-1),i=1..nops(L)))
%p A064507 end proc:
%p A064507 select(filter, [seq(i,i=11..2000,2)]); # _Robert Israel_, Dec 04 2016
%o A064507 (PARI) isok(n) = (n>=10) && isprime(fromdigits(digits(n), n)); \\ _Michel Marcus_, Dec 04 2016
%Y A064507 Cf. A064508.  Contained in A054684.
%K A064507 nonn,base
%O A064507 1,1
%A A064507 _Jon Perry_, Oct 06 2001
%E A064507 Offset corrected by _Arkadiusz Wesolowski_, Oct 19 2013
%E A064507 Name corrected by _Robert Israel_, Dec 04 2016