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 A166923 #9 Feb 03 2025 13:51:52
%S A166923 4,9,7,4,4,7,1,1,7,4,7,1,7,4,4,1,7,4,7,1,1,4,4,1,4,4,7,1,1,7,1,7,4,7,
%T A166923 7,4,7,1,7,4,1,1,4,7,1,1,7,4,4,7,1,7,4,1,7,4,1,1,4,4,7,7,1,7,4,4,4,7,
%U A166923 7,4,4,1,4,7,1,7,4,1,7,7,7,4,1,1,4,4,1,4,4,7,1,4,1,7,7,1,7,1,1,1,4,1,7,4,7
%N A166923 Digital root of prime(n)^2.
%t A166923 Table[If[(m9=Mod[Prime[n]^2,9])==0,9,m9],{n,200}]
%o A166923 (Python)
%o A166923 from sympy import prime
%o A166923 def A166923(n):
%o A166923 return 1 + (prime(n)**2-1) % 9 # _Chai Wah Wu_, Sep 03 2014
%Y A166923 Cf. A010888, A038194.
%K A166923 base,nonn
%O A166923 1,1
%A A166923 _Zak Seidov_, Oct 23 2009
%E A166923 Definition corrected by _Chai Wah Wu_, Sep 03 2014