A073544 Numbers k such that 1/(1/phi(k) + 1/phi(k+1) + 1/phi(k+2) + 1/phi(k+3)) is an integer.

13, 75, 111, 144, 192, 558, 559, 1683, 2016, 3624, 7129, 10369, 11658, 18362, 19442, 19800, 19801, 32772, 47627, 60482, 82082, 133988, 143642, 229321, 291721, 312483, 352846, 390603, 395136, 436801, 465482, 600601, 711936, 806736, 819729

Offset

1,1

Links

Table of n, a(n) for n=1..35.

Example

1/phi(75)+1/phi(76)+1/phi(77)+1/phi(78) = 1/40+1/36+1/60+1/24 = 1/9 so 75 is in the sequence.

Mathematica

Select[Range[900000], IntegerQ[1/Sum[1/EulerPhi[ #+i], {i, 0, 3}]]&]

Prog

(PARI) isok(k) = numerator(1/eulerphi(k) + 1/eulerphi(k+1) + 1/eulerphi(k+2) + 1/eulerphi(k+3)) == 1; \\ Michel Marcus, Feb 18 2021

Crossrefs

Cf. A000010, A073542, A073543.

Sequence in context: A301882 A302079 A103968 * A051361 A114070 A005340

Adjacent sequences: A073541 A073542 A073543 * A073545 A073546 A073547

Keyword

nonn

Author

Benoit Cloitre, Aug 27 2002

Extensions

Edited by Dean Hickerson, Sep 03 2002

Status

approved