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 A284757 Number of solutions to Nickerson variant of quadruples version of Langford (or Langford-Skolem) problem. 2
 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 10, 55, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,24 COMMENTS How many ways are of arranging the numbers 1,1,1,1,2,2,2,2,3,3,3,3,...,n,n,n,n so that there are zero numbers between the first and second 1's, between the second and third 1's and between the third and fourth 1's; one number between the first and second 2's, between the second and third 2's and between the third and fourth 2's; ... n-1 numbers between the first and second n's, between the second and third n's and between the third and fourth n's? An equivalent definition is A261517 with added condition that all different common intervals are <= n. a(n) ignores reflected solutions. LINKS Table of n, a(n) for n=1..31. Fausto A. C. Cariboni, Solutions for a(24)-a(25) J. E. Miller, Langford's Problem. FORMULA a(n) = 0 if (n mod 8) not in {0, 1}. - Max Alekseyev, Sep 28 2023 CROSSREFS Cf. A014552, A059106, A059108, A261517. Sequence in context: A198770 A222539 A219623 * A303608 A139610 A088404 Adjacent sequences: A284754 A284755 A284756 * A284758 A284759 A284760 KEYWORD nonn,more AUTHOR Fausto A. C. Cariboni, Apr 02 2017 EXTENSIONS a(28)-a(31) from Max Alekseyev, Sep 24 2023 STATUS approved

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Last modified August 10 09:30 EDT 2024. Contains 375044 sequences. (Running on oeis4.)