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

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

1,1

Links

Table of n, a(n) for n=1..33.

Example

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

Mathematica

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

Prog

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

Crossrefs

Cf. A000010, A076529, A220160.

Sequence in context: A217727 A071008 A299535 * A178077 A218148 A112535

Adjacent sequences: A220166 A220167 A220168 * A220170 A220171 A220172

Keyword

nonn

Author

Carl Najafi, Dec 06 2012

Extensions

More terms from Amiram Eldar, Aug 12 2019

Status

approved