login
A073543
Numbers k such that 1/(1/phi(k) + 1/phi(k+1) + 1/phi(k+2)) is an integer.
6
12, 36, 37, 72, 73, 86, 95, 181, 192, 482, 540, 541, 560, 637, 813, 1152, 1620, 1621, 1683, 2017, 2101, 2283, 2557, 2592, 2642, 2916, 3031, 3032, 3061, 3381, 3624, 3625, 4357, 5077, 5186, 5581, 6337, 6661, 7417, 8100, 9118, 9181, 9299, 9720, 9901
OFFSET
1,1
LINKS
EXAMPLE
1/phi(2283)+1/phi(2284)+1/phi(2285) = 1/1520+1/1140+1/1824 = 1/480 so 2283 is in the sequence.
MATHEMATICA
Select[Range[10000], IntegerQ[1/Sum[1/EulerPhi[ #+i], {i, 0, 2}]]&]
PROG
(PARI) isok(k) = numerator(1/eulerphi(k) + 1/eulerphi(k+1) + 1/eulerphi(k+2)) == 1; \\ Michel Marcus, Feb 18 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Aug 27 2002
EXTENSIONS
Edited by Dean Hickerson, Sep 03 2002
STATUS
approved