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%I #43 Sep 06 2019 14:51:39
%S 1,2,5,6,7,11,15,712,7599,13280
%N Numbers k such that the reverse of the first k digits in the decimal expansion of Pi forms a prime.
%C The initial digits of a few corresponding primes are in A007523. The last one a(10)=768556......62951413 is a prime with 13280-digit. That is A092845(13279).
%e 1 is a term as the first digit of pi, 3, reversed is prime. 2 is a term as the first two digits of pi, 31, reversed is prime. 3 is not a term as the first three digits of pi, 314, reversed, is not prime. - _David A. Corneth_, Feb 13 2017
%t Do[If[PrimeQ[FromDigits[Reverse[IntegerDigits[Floor[Pi*10^(n - 1)]]]]],Print[n]],{n, 13335}]
%t Module[{pid=RealDigits[Pi,10,20000][[1]]},Select[Range[16000],PrimeQ[ FromDigits[ Reverse[Take[pid,#]]]]&]] (* _Harvey P. Dale_, Sep 06 2019 *)
%Y Cf. A092845, A007523, A011545.
%K nonn,more,base,less
%O 1,2
%A _XU Pingya_, Feb 13 2017
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