A071259 -id:A071259 - cp's OEIS frontend

A071260 Integer part of the geometric mean of the n-th prime prime(n) and the n-th composite number C(n).

2, 4, 6, 7, 10, 12, 15, 16, 19, 22, 24, 27, 30, 32, 34, 37, 39, 41, 44, 47, 49, 51, 53, 56, 60, 62, 64, 67, 69, 71, 76, 79, 81, 83, 87, 88, 92, 94, 96, 99, 101, 104, 108, 110, 112, 113, 118, 123, 125, 126, 129, 132, 134, 138, 140, 143, 146, 148, 150, 153, 155, 158

Offset: 0

Amarnath Murthy, May 30 2002

nonn

			a(7) =floor {prime(7)*C(7)}^(1/2) = (17*14)^1/2 = 15.

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Cf. A071259.

Module[{nn=100,prs,cmps,len},prs=Prime[Range[nn]];cmps=Select[ Range[ nn+Length[prs]],CompositeQ];len=Min[Length[cmps],Length[prs]];IntegerPart[ GeometricMean[#]]&/@Thread[{Take[prs,len],Take[ cmps,len]}]] (* Harvey P. Dale, Aug 12 2016 *)

Floor [ {prime(n)* C(n)}^(1/2)]

More terms from Hans Havermann, Sep 23 2002

A073465 Numbers n such that phi(n)/pi(n) is an integer.

Original entry on oeis.org

2, 3, 4, 8, 10, 11, 13, 14, 20, 27, 37, 39, 43, 63, 90, 91, 95, 122, 124, 136, 152, 169, 175, 176, 224, 322, 364, 365, 410, 460, 605, 875, 917, 1082, 1084, 1085, 1086, 1087, 1137, 1143, 1164, 1168, 1444, 1517, 1541, 1751, 1786, 1991, 2873, 3087, 3101, 3283

Offset: 1

Labos Elemer, Aug 02 2002

nonn

Donovan Johnson, Table of n, a(n) for n = 1..1000

Cf. A000010, A000720, A073464.

Select[Range[2,3300],IntegerQ[EulerPhi[#]/PrimePi[#]]&] (* Harvey P. Dale, Apr 11 2020 *)

Mod[A000010(n), A000720(n)]=A071259[n]=0

cp's OEIS Frontend

A071260 Integer part of the geometric mean of the n-th prime prime(n) and the n-th composite number C(n).

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