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 A138758 #7 Apr 10 2021 22:23:44 %S A138758 2,4,0,0,0,0,0,0,1,0,2,0,0,1,0,0,1,1,1,1,0,0,1,0,0,0,2,6,0,0,1,0,0,0, %T A138758 0,1,1,0,2,3,0,0,0,0,0,4,0,1,2,4,0,1,0,0,0,0,0,0,2,0,0,0,0,0,1,0,0,0, %U A138758 0,3,1,1,2,0,1,0,0,0,0,0,0,0,0,0,1,1,0,0,0,1,0,0,1,0,2,0,1,0,0,0,1,3,0,0,1 %N A138758 Index of A001203(n) (continued fraction for Pi) in A000040 (primes), or 0 if A001203(n) is not prime. %F A138758 a(n) = A000720(A001203(n)) * A010051(A001203(n)). %e A138758 This sequence starts 2,4,0,0,... since the 1st and 2nd terms of the continued fraction expansion of Pi, A001203 = (3, 7, 15, 1, ...) are the 2nd resp. 4th primes, while the next two terms are not primes. %o A138758 (PARI) default(realprecision,1000); t=contfrac(Pi); vector(#t,i,isprime(t[i])*primepi(t[i])) %Y A138758 Cf. A001203, A138757, A138759, A005042. %K A138758 nonn %O A138758 1,1 %A A138758 _M. F. Hasler_, Mar 31 2008