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A109607 Sum of coprimes of n greater than 1. 1
0, 0, 0, 2, 3, 9, 5, 20, 15, 26, 19, 54, 23, 77, 41, 59, 63, 135, 53, 170, 79, 125, 109, 252, 95, 249, 155, 242, 167, 405, 119, 464, 255, 329, 271, 419, 215, 665, 341, 467, 319, 819, 251, 902, 439, 539, 505, 1080, 383, 1028, 499, 815, 623, 1377, 485, 1099, 671, 1025 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..57.

FORMULA

a(n) = A023896(n) - 1. - Joerg Arndt, Mar 08 2013

G.f.: -x/(1 - x) + Sum_{k>=1} mu(k)*k*x^k/(1 - x^k)^3. - Ilya Gutkovskiy, May 28 2019

EXAMPLE

a(9) = 26 because 2,4,5,7,8 are coprime to 9 and 2+4+5+7+8 = 26.

PROG

(PARI) a(n) = sum(i=2, n-1, i*(gcd(i, n)==1)); \\ Michel Marcus, Mar 08 2013

(PARI) a(n)=if(n<3, 0, n*eulerphi(n)/2-1) \\ Charles R Greathouse IV, Mar 08 2013

CROSSREFS

Sequence in context: A120725 A253046 A324576 * A324581 A127612 A038756

Adjacent sequences:  A109604 A109605 A109606 * A109608 A109609 A109610

KEYWORD

nonn

AUTHOR

Andrew Weimholt, Jul 31 2005

EXTENSIONS

Added "greater than 1" to name to match terms, Joerg Arndt, Mar 08 2013

STATUS

approved

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Last modified August 18 04:50 EDT 2019. Contains 326072 sequences. (Running on oeis4.)