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 A065991 #11 Aug 14 2025 15:48:31
%S A065991 1,62,3253,4490,62622
%N A065991 Numbers k such that the first k base-4 digits of Pi expressed in decimal forms a prime.
%C A065991 a(6) > 10^5. - _Michael S. Branicky_, Aug 14 2025
%e A065991 The first 62 quaternary digits of Pi (A004603) are 30210033312222020201122030020310301030121202202320003130013031 = 16703571626015105435307505830654230989 in decimal, which is a prime.
%t A065991 Do[ If[ PrimeQ[ FromDigits[ First[ RealDigits[Pi, 4, n]], 4]], Print[n]], {n, 1, 4000} ]
%Y A065991 Cf. A004603, A060421.
%K A065991 base,nonn,more
%O A065991 1,2
%A A065991 _Robert G. Wilson v_, Dec 10 2001
%E A065991 a(4) from _Pontus von Brömssen_, Aug 02 2025
%E A065991 a(5) from _Michael S. Branicky_, Aug 13 2025