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 A126991 #10 Jan 25 2021 15:25:24
%S A126991 3,5,7,11,13,19,19,23,29,31,37,43,47,47,53,61,61,67,73,79,83,89,89,97,
%T A126991 101,103,113,113,113,113,137,139,139,149,157,157,167,167,173,181,181,
%U A126991 181,199,199,211,211,211,229,233,239,241,241,251,257,263,271,271,281
%N A126991 Prime preceding the geometric mean of prime(n-2) and prime(n+2).
%t A126991 << NumberTheory`NumberTheoryFunctions` a = {}; Do[AppendTo[a,PreviousPrime[Sqrt[(Prime[x - 2])*(Prime[x + 2])]]], {x, 3, 100}]; a
%t A126991 Table[NextPrime[GeometricMean[{Prime[n-2],Prime[n+2]}],-1],{n,3,60}] (* _Harvey P. Dale_, May 14 2015 *)
%o A126991 (PARI) A126991(n)={ n=sqrtint(prime(n-2)*prime(n+2)); if(0==n%2, n--); while(!isprime(n), n-=2); n } /* then vector(50,n,A126991(n+2)) displays a list of values ; t=3;forprime(p=2,999, while(A126991(t)<p,t++);if(A126991(t)>p,print(p))) prints primes 2,17,41,59,... not in this sequence */ \\ _M. F. Hasler_, Jun 14 2007
%Y A126991 Cf. A126990, A126992, A124662.
%K A126991 nonn,easy,less
%O A126991 3,1
%A A126991 _Artur Jasinski_, Jan 01 2007
%E A126991 Edited by _M. F. Hasler_, Jun 14 2007