A065987 - OEIS

%I #14 Sep 18 2024 06:49:29

%S 2,23,31,35,124,323,2787,5717,6506,8980,106817,109773,125244

%N Numbers k such that the first k binary digits of Pi expressed in decimal forms a prime.

%e The first 23 binary digits of Pi (A004601) are 11001001000011111101101 = 6588397 in decimal, which is a prime.

%t Do[ If[ PrimeQ[ FromDigits[ First[ RealDigits[Pi, 2, n]], 2]], Print[n]], {n, 1, 7000} ]

%Y Cf. A004601, A117721 (the primes themselves).

%K base,nonn,more,changed

%O 1,1

%A _Robert G. Wilson v_, Dec 10 2001

%E a(10) from _Hans Havermann_, Jul 23 2006

%E a(11) from _Hans Havermann_, Sep 06 2006

%E a(12)-a(13) from _Michael S. Branicky_, Sep 17 2024