A290704 Solutions to 2*x - phi(x) = sigma(x)/2, where phi(x) is the Euler totient function of x.
1680, 4200, 27000, 175392, 282960, 707400, 1668480, 3344544, 5658480, 14146200, 48644064, 90008880, 130110624, 225022200, 357994728, 460763160, 607281696, 1926458352, 3830537880, 5857651296, 7840881216, 8414628480, 8704032876, 8843224500, 14279194512, 29522053080
Offset: 1
Keywords
Examples
phi(1680) = 384, sigma(1680) = 5952 and 2*1680 - 384 = 2976 = 5952/2.
References
- Like A099650 but with totient phi(x) replaced by cototient x - phi(x).
Programs
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Maple
with(numtheory): P:=proc(q) local n; for n from 1 to q do if 2*n-phi(n)=sigma(n)/2 then print(n); fi; od; end: P(10^9);
Extensions
a(10)-a(26) from Giovanni Resta, Aug 25 2017