A121048 a(n) = n + phi(n), where phi is the Euler totient function.
2, 3, 5, 6, 9, 8, 13, 12, 15, 14, 21, 16, 25, 20, 23, 24, 33, 24, 37, 28, 33, 32, 45, 32, 45, 38, 45, 40, 57, 38, 61, 48, 53, 50, 59, 48, 73, 56, 63, 56, 81, 54, 85, 64, 69, 68, 93, 64, 91, 70, 83, 76, 105, 72, 95, 80, 93, 86, 117, 76, 121, 92, 99, 96, 113, 86, 133, 100, 113
Offset: 1
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Programs
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Magma
[n + EulerPhi(n): n in [1..70]]; // Vincenzo Librandi, Jul 13 2012
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Mathematica
Table[n+EulerPhi[n],{n,1,70}] -
PARI
a(n) = n+eulerphi(n); \\ Michel Marcus, Sep 19 2022
Formula
a(n) = n + phi(n) = n + A000010(n).
Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = 1 + 1/zeta(2) = 1.607927... . - Amiram Eldar, Dec 16 2023