OFFSET
1,3
COMMENTS
This sequence gives the row length of the irregular triangle A337936 (complete system of tripling sequences modulo N(n)).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Lv Chuan, On the Mean Value of an Arithmetical Function, in Zhang Wenpeng (ed.), Research on Smarandache Problems in Number Theory (collected papers), 2004, pp. 89-92.
FORMULA
a(n) ~ (9/(4*Pi^2))*n^2 + O(n^(3/2+eps)) (Lv Chuan, 2004). - Amiram Eldar, Aug 02 2022
EXAMPLE
The pairs [n, N(n)], n >= 1, begin:
[1, 1], [2, 2], [3, 4], [4, 5], [5, 7], [6, 8], [7, 10], [8, 11], [9, 13], [10, 14], [11, 16], [12, 17], [13, 19], [14, 20], [15, 22], [16, 23], [17, 25], [18, 26], [19, 28], [20, 29], ...
MATHEMATICA
a[n_] := EulerPhi[Floor[(3*n - 1)/2]]; Array[a, 100] (* Amiram Eldar, Oct 22 2020 *)
PROG
(PARI) a(n) = eulerphi((3*n-1)\2); \\ Michel Marcus, Oct 22 2020
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wolfdieter Lang, Oct 22 2020
STATUS
approved