%I #7 Oct 01 2012 12:16:25

%S 7,19,31,41,43,79,89,107,137,157,197,233,263,271,293,317,367,379,433,

%T 449,479,491,499,601,641,653,673,751,757,761,769,787,797,821,823,827,

%U 853,887

%N In the decimal expansion of Pi, the first occurrence of these primes begins at a prime position.

%C We label the positions in 3.14159... so that 1 is in position 1, 4 in position 2, 1 in position 3, 5 in position 4, and so on.

%e The first 19 in the decimal expansion of Pi (see A000796) starts in position 37, which is a prime.

%t pos_in_Pi={1,6,9,2,4,7,13,11,5,49,94,148,110,1,3,....};

%t s={};Do[If[PrimeQ[x]&&PrimeQ[pos_in_Pi[[x]]],AppendTo[s,pos_in_Pi]],{x,Length[v]}];s

%Y Cf. A000796.

%K nonn,base

%O 1,1

%A _Vicente Izquierdo Gomez_, Sep 01 2012

%E Edited by _N. J. A. Sloane_, Sep 09 2012