The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A215977 Number T(n,k) of simple unlabeled graphs on n nodes with exactly k connected components that are trees or cycles; triangle T(n,k), n >= 0, 0 <= k <= n, read by rows. 13
 1, 0, 1, 0, 1, 1, 0, 2, 1, 1, 0, 3, 3, 1, 1, 0, 4, 5, 3, 1, 1, 0, 7, 10, 6, 3, 1, 1, 0, 12, 17, 12, 6, 3, 1, 1, 0, 24, 33, 23, 13, 6, 3, 1, 1, 0, 48, 62, 47, 25, 13, 6, 3, 1, 1, 0, 107, 127, 92, 53, 26, 13, 6, 3, 1, 1, 0, 236, 267, 189, 106, 55, 26, 13, 6, 3, 1, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,8 LINKS Alois P. Heinz, Rows n = 0..140, flattened EXAMPLE T(4,1) = 3: .o-o. .o-o. .o-o. .| |. .| . .|\ . .o-o. .o-o. .o o. . T(4,2) = 3: .o-o. .o-o. .o-o. .|/ . .| . . . .o o. .o o. .o-o. . T(5,1) = 4: .o-o-o. .o-o-o. .o-o-o. .o-o-o. .| / . .| . .| | . . /| . .o-o . .o-o . .o o . .o o . . T(5,2) = 5: .o-o o. .o-o o. .o-o o. .o o-o. .o o-o. .| | . .| . .|\ . .|\ . .| . .o-o . .o-o . .o o . .o-o . .o-o . Triangle T(n,k) begins: 1; 0, 1; 0, 1, 1; 0, 2, 1, 1; 0, 3, 3, 1, 1; 0, 4, 5, 3, 1, 1; 0, 7, 10, 6, 3, 1, 1; 0, 12, 17, 12, 6, 3, 1, 1; ... MATHEMATICA b[n_] := b[n] = If[n <= 1, n, Sum[Sum[d*b[d], {d, Divisors[j]}]*b[n-j], {j, 1, n-1}]/(n-1)]; g[n_] := g[n] = If[n>2, 1, 0]+b[n]-(Sum [b[k]*b[n-k], {k, 0, n}] - If[Mod[n, 2] == 0, b[n/2], 0])/2; p[n_, i_, t_] := p[n, i, t] = If[n2 else 0) + b(n) - (sum(b(k)*b(n - k) for k in range(n + 1)) - (b(n//2) if n%2==0 else 0))//2 @cacheit def p(n, i, t): return 0 if n

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

Last modified May 31 23:09 EDT 2023. Contains 363068 sequences. (Running on oeis4.)