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 A199890 Number of compositions of n such that the number of parts and the largest part and the smallest part are pairwise coprime. 2
 1, 1, 1, 6, 4, 15, 37, 81, 133, 270, 565, 1200, 2449, 4961, 10014, 20083, 39585, 77566, 152934, 305587, 617857, 1257333, 2558837, 5180712, 10404918, 20732162, 41087390, 81291644, 161136101, 320733232, 641408052, 1287453960, 2589099670, 5207066575, 10459270462 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS Alois P. Heinz, Table of n, a(n) for n = 1..250 EXAMPLE a(4) = 6: [1,1,1,1], [1,1,2], [1,2,1], [1,3], [2,1,1], [3,1]. MAPLE b:= proc(n, t, g, k) option remember; `if`(n=0, `if`(igcd(g, t)=1 and igcd(k, t)=1 and igcd(g, k)=1, 1, 0), add(b(n-i, t+1, max(i, g), min(i, k)), i=1..n)) end: a:= n-> b(n, 0, 0, infinity): seq(a(n), n=1..40); MATHEMATICA b[n_, t_, g_, k_] := b[n, t, g, k] = If[n == 0, If[GCD[g, t] == 1 && GCD[k, t] == 1 && GCD[g, k] == 1, 1, 0], Sum[b[n-i, t+1, Max[i, g], Min[i, k]], {i, 1, n}]]; a[n_] := b[n, 0, 0, Infinity]; Table[a[n], {n, 1, 40}] (* Jean-François Alcover, Nov 05 2014, after Alois P. Heinz *) CROSSREFS Cf. A201218. Sequence in context: A064462 A248266 A325689 * A198459 A083581 A171089 Adjacent sequences: A199887 A199888 A199889 * A199891 A199892 A199893 KEYWORD nonn AUTHOR Alois P. Heinz, Nov 11 2011 STATUS approved

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Last modified September 22 08:04 EDT 2023. Contains 365519 sequences. (Running on oeis4.)