A109046 - OEIS

A109046

a(n) = lcm(n, 5).

0, 5, 10, 15, 20, 5, 30, 35, 40, 45, 10, 55, 60, 65, 70, 15, 80, 85, 90, 95, 20, 105, 110, 115, 120, 25, 130, 135, 140, 145, 30, 155, 160, 165, 170, 35, 180, 185, 190, 195, 40, 205, 210, 215, 220, 45, 230, 235, 240, 245, 50, 255, 260, 265, 270, 55, 280, 285, 290

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OFFSET

0,2

LINKS

Amiram Eldar, Table of n, a(n) for n = 0..10000

Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,2,0,0,0,0,-1).

Index entries for sequences related to lcm's.

FORMULA

a(n) = n*5/gcd(n, 5) = 5*n/A109009(n) = 5*A060791(n).

G.f.: 5*x*(x^4+x^3+3*x^2+x+1)*(x^4+x^3-x^2+x+1) / ( (x-1)^2*(x^4+x^3+x^2+x+1)^2 ). - R. J. Mathar, Apr 18 2011

Sum_{k=1..n} a(k) ~ (21/10) * n^2. - Amiram Eldar, Nov 26 2022

Sum_{n>=1} (-1)^(n+1)/a(n) = 9*log(2)/25. - Amiram Eldar, Sep 08 2023