login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS").
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A268756 Number of triples x, y, r such that r divides x*y, r divides at least one of x or y, and x*y <= n. 1
1, 5, 9, 17, 21, 35, 39, 53, 61, 75, 79, 107, 111, 125, 139, 160, 164, 192, 196, 224, 238, 252, 256, 304, 312, 326, 340, 368, 372, 418, 422, 452, 466, 480, 494, 550, 554, 568, 582, 630, 634, 680, 684, 712, 740, 754, 758, 830, 838, 866, 880, 908, 912, 960, 974 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) - a(n - 1) only depends on the prime signature of n. - David A. Corneth, Aug 30 2018

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

David A. Corneth, PARI prog

Adrian W. Dudek, On the Success of Mishandling Euclid's Lemma, arXiv:1602.03555 [math.HO], 2016. See A(n) p. 2.

Adrian W. Dudek, On the Success of Mishandling Euclid's Lemma, The American Mathematical Monthly, Vol. 123, No. 9 (2016), 924-927.

PROG

(PARI) a(n) = {s = 0; for (x=1, n, for (y = 1, n, if (x*y <= n, s += sum(r = 1, x*y, !(x*y % r) && (!(x % r) || !(y % r))); ); ); ); s; }

(PARI) \\ See PARI link \\ David A. Corneth, Aug 30 2018

CROSSREFS

Cf. A061502, A268732.

Sequence in context: A022341 A255651 A216877 * A095725 A005006 A276194

Adjacent sequences:  A268753 A268754 A268755 * A268757 A268758 A268759

KEYWORD

nonn

AUTHOR

Michel Marcus, Feb 13 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 1 21:42 EST 2020. Contains 338858 sequences. (Running on oeis4.)