This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A138759 #7 Aug 07 2019 13:25:48 %S A138759 1,2,9,11,14,17,18,19,20,23,27,28,31,36,37,39,40,46,48,49,50,52,59,65, %T A138759 70,71,72,73,75,85,86,90,93,95,97,101,102,105,106,109,110,111,118,120, %U A138759 122,123,124,127,128,131,132,133,140,142,145,146,151,152,153,155,159 %N A138759 Indices for which A001203 (continued fraction for Pi) is prime. %F A138759 k is in A138759 <=> A001203(k) is in A000040 %e A138759 This sequence starts 1,2,9,11,... since the first, 2nd, 9th, 11th... %e A138759 term of sequence A001203 = (3, 7, 15, 1, 292, 1, 1, 1, 2, ...) are primes. %t A138759 Position[ContinuedFraction[Pi,200],_?PrimeQ]//Flatten(* _Harvey P. Dale_, Aug 07 2019 *) %o A138759 (PARI) default(realprecision,1000); t=contfrac(Pi); for( k=1,#t, isprime(t[k]) & print1(k",")) %Y A138759 Cf. A001203, A005042, A107892, A138758. %K A138759 nonn %O A138759 1,2 %A A138759 _M. F. Hasler_, Mar 31 2008