A126991 Prime preceding the geometric mean of prime(n-2) and prime(n+2).
3, 5, 7, 11, 13, 19, 19, 23, 29, 31, 37, 43, 47, 47, 53, 61, 61, 67, 73, 79, 83, 89, 89, 97, 101, 103, 113, 113, 113, 113, 137, 139, 139, 149, 157, 157, 167, 167, 173, 181, 181, 181, 199, 199, 211, 211, 211, 229, 233, 239, 241, 241, 251, 257, 263, 271, 271, 281
Offset: 3
Programs
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Mathematica
<< NumberTheory`NumberTheoryFunctions` a = {}; Do[AppendTo[a,PreviousPrime[Sqrt[(Prime[x - 2])*(Prime[x + 2])]]], {x, 3, 100}]; a Table[NextPrime[GeometricMean[{Prime[n-2],Prime[n+2]}],-1],{n,3,60}] (* Harvey P. Dale, May 14 2015 *) -
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)
Extensions
Edited by M. F. Hasler, Jun 14 2007