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 A056972 Number of (binary) heaps on n levels (i.e., of 2^n - 1 elements). 5
 1, 1, 2, 80, 21964800, 74836825861835980800000, 2606654998899867556195703676289609067340669424836280320000000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS A sequence {a_i}_{i=1..N} forms a (binary) heap if it satisfies a_i (2^n-1)!/mul((2^k-1)^(2^(n-k)), k=1..n): seq(a(i), i=0..6);  # Alois P. Heinz, Nov 22 2007 MATHEMATICA s[1] := 1; s[l_] := s[l] := Binomial[2^l-2, 2^(l-1)-1]s[l-1]^2; Table[s[l], {l, 10}] CROSSREFS Cf. A000225, A056971, A195581. Column k=2 of A273712. Sequence in context: A156932 A291331 A293290 * A051391 A041799 A187858 Adjacent sequences:  A056969 A056970 A056971 * A056973 A056974 A056975 KEYWORD nonn AUTHOR STATUS approved

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Last modified August 20 09:56 EDT 2019. Contains 326143 sequences. (Running on oeis4.)