A076529 -id:A076529 - cp's OEIS frontend

A220160 Numbers n for which phi(n) = phi(n-1) - phi(n+1).

194, 3530, 9338, 27230, 46794, 78182, 90194, 112994, 135014, 437184, 849404, 935220, 1078580, 1283600, 1986974, 2209584, 2341184, 2411174, 2689694, 2744144, 3619070, 3712544, 4738184, 5132984, 6596120, 7829030, 8184714, 12176108, 12292004, 13342958, 26400842

Offset: 1

Carl Najafi, Dec 06 2012

nonn

			phi(3529) - phi(3531) = 3528 - 2120 = 1408 = phi(3530).

Donovan Johnson, Table of n, a(n) for n = 1..100

Cf. A000010, A076529.

Select[Range[10^6], EulerPhi[#] == EulerPhi[# - 1] - EulerPhi[# + 1] &]
With[{ep=EulerPhi[Range[27500000]]},Flatten[Position[Partition[ ep,3,1], ?(#[[1]]- #[[3]]==#[[2]]&),{1},Heads->False]]]+1 (* _Harvey P. Dale, Feb 04 2015 *)

A220169 Numbers n for which phi(n^2) = phi(n-1) * phi(n+1).

Original entry on oeis.org

2, 4, 16, 256, 976, 3256, 5188, 11716, 13366, 22936, 65536, 307396, 491536, 589408, 983776, 1659586, 2822716, 3137356, 5577826, 6475456, 7378372, 8698096, 10798726, 32235736, 37797436, 39220126, 39285436, 51555136, 52077196, 56992552, 63767926, 70075996, 82391002

Offset: 1

Carl Najafi, Dec 06 2012

nonn

			phi(976^2) = 468480 = 480*976 = phi(975)*phi(977).

Cf. A000010, A076529, A220160.

Select[Range[10^6], EulerPhi[#^2] == EulerPhi[# - 1] EulerPhi[# + 1] &]

isok(n) = eulerphi(n^2) == eulerphi(n-1) * eulerphi(n+1); \\ Michel Marcus, Aug 12 2019

More terms from Amiram Eldar, Aug 12 2019

cp's OEIS Frontend

A220160 Numbers n for which phi(n) = phi(n-1) - phi(n+1).

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