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A143270 a(n) = n*A002088. 3
1, 4, 12, 24, 50, 72, 126, 176, 252, 320, 462, 552, 754, 896, 1080, 1280, 1632, 1836, 2280, 2560, 2940, 3300, 3956, 4320, 5000, 5512, 6210, 6776, 7830, 8340, 9548, 10368, 11352, 12240, 13440, 14256, 15984, 17100, 18486, 19600, 21730, 22764, 25112 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also number of reduced fractions with denominators <= n and values between 1/n and n (inclusive). [From Reinhard Zumkeller, Jan 15 2009]

LINKS

Table of n, a(n) for n=1..43.

FORMULA

a(n) = n*A002088, where A002088 = partial sums of phi(n). Equals row sums of triangle A143269.

a(n) = SUM(SUM(0^(GCD(i,j)-1): 1<=j<=i*n): 1<=i<=n). [From Reinhard Zumkeller, Jan 15 2009]

EXAMPLE

a(4) = 24 = n*A002088(n) = 4*6.

a(4) = 24 = sum of row 4 terms of triangle A143269: (4 + 4 + 8 + 8).

a(3) = #{1/3,1/2,2/3,1,4/3,3/2,5/3,2,7/3,5/2,8/3,3} = 12. [From Reinhard Zumkeller, Jan 15 2009]

CROSSREFS

Cf. A000010, A002088, A143269.

Sequence in context: A102652 A279626 A238607 * A037338 A136486 A003203

Adjacent sequences:  A143267 A143268 A143269 * A143271 A143272 A143273

KEYWORD

nonn

AUTHOR

Gary W. Adamson, Aug 03 2008

EXTENSIONS

More terms from Reinhard Zumkeller, Jan 15 2009

STATUS

approved

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Last modified December 5 22:37 EST 2019. Contains 329782 sequences. (Running on oeis4.)