A083250 - OEIS

%I #14 Jan 27 2019 05:45:53

%S 3,825,1755,4641,5313,56865,58395,140049,159152763,361701435

%N Numbers n for which abs(A045763(n) - A073757(n)) = 3, i.e., signed difference of size of related and unrelated sets to n equals either 3 or -3.

%C No more terms below 10^9. - _Amiram Eldar_, Jan 27 2019

%e For n=140049: d=40 divisors, r=70026 coprimes and u=70023 unrelated numbers to n; abs(r-u) = 3.

%t Do[r=EulerPhi[n]; d=DivisorSigma[0, n]; u=n-r-d+1; df=2*u-n; If[Equal[Abs[df], 3], Print[n(*, {d, r, u}*)]], {n, 1, 100}]

%o (PARI) isok(n) = abs(n-2*eulerphi(n)-2*numdiv(n)+2) == 3; \\ _Michel Marcus_, Jul 30 2017

%Y Cf. A000005, A000010, A045763, A073757, A083243-A083249.

%K nonn,more

%O 1,1

%A _Labos Elemer_, May 07 2003

%E a(9)-a(10) from _Amiram Eldar_, Jan 27 2019