OFFSET
1,2
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..1000
MAPLE
with(numtheory): A015840:=n->`if`(sigma(n+3) mod phi(n) = 0, n, NULL): seq(A015840(n), n=1..5*10^3); # Wesley Ivan Hurt, Feb 04 2017
MATHEMATICA
Select[Range[3000], Divisible[DivisorSigma[1, 3 + #], EulerPhi[#]] &] (* David Nacin, Mar 03 2012 *)
PROG
(PARI) is(n)=!(sigma(n+3)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
a(1) = 1 inserted by Ivan Neretin, Jan 30 2017
STATUS
approved