This site is supported by donations to The OEIS Foundation.



Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A002968 Number of pairings {(b[1],c[1]),(b[2],c[2]),...,(b[n],c[n])} of the first 2n positive integers satisfying b[i] < c[i] and such that the 2n numbers c[i]+b[i] and c[i]-b[i] are all distinct.
(Formerly M4494)
1, 1, 0, 1, 8, 22, 51, 342, 2609, 16896, 99114, 876579, 8551800, 79595269, 764804085, 8905825760 (list; graph; refs; listen; history; text; internal format)



Huff paper has a typographical error, a(8)=2669. - Sean A. Irvine, Dec 14 2014


N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

R. Spira, Noncomplete residue systems, Problem 71-4, SIAM Rev., 14 (1972), 173ff.


Table of n, a(n) for n=0..15.

R. K. Guy, Letter to G. B. Huff & N. J. A. Sloane, Aug 1974

G. B. Huff, On pairings of the first 2n natural numbers, Acta Arithmetica, 23 (1973), 117-126.

D. A. Klarner, Letter to N. J. A. Sloane, Mar 1974

R. Spira, Noncomplete residue system Problem 71-4, SIAM Rev., 14 (1972), 173-174. (Annotated scanned copy)


Cf. A007631.

Sequence in context: A305181 A048489 A124701 * A211530 A058404 A211479

Adjacent sequences:  A002965 A002966 A002967 * A002969 A002970 A002971




N. J. A. Sloane.


Better definition and values of a(11)-a(15) from Sean A. Irvine, Dec 14 2014

a(0)=1 prepended by Alois P. Heinz, Oct 05 2018



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 8 04:31 EST 2019. Contains 329850 sequences. (Running on oeis4.)