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A109055 To compute a(n) we first write down 3^n 1's in a row. Each row takes the rightmost 3rd part of the previous row and each element in it equals sum of the elements of the previous row starting with the first of the rightmost 3rd part. The single element in the last row is a(n). 6
1, 1, 3, 24, 541, 35649, 6979689, 4085743032, 7166723910237, 37698139930450365, 594816080266215640710, 28154472624850002001979592, 3997853576535778666975681355079, 1703042427700923785323670557504832751 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Comment from Franklin T. Adams-Watters, Jul 13 2006: This is the number of subpartitions of the sequence 3^n-1. As such it can also be computed adding forward, with 3^n terms in the n-th line:

1...........................................................................

1.1 1.......................................................................

1.2.3.3..3..3..3..3..3......................................................

1.3.6.9.12.15.18.21.24.24.24.24.24.24.24.24.24.24.24.24.24.24.24.24.24.24.24

LINKS

Table of n, a(n) for n=0..13.

EXAMPLE

For example, for n=3 the array looks like this:

1..1..1..1..1........1..1..1..1..1..1..1..1..1..1

........................1..2..3..4..5..6..7..8..9

..........................................7.15.24

...............................................24

Therefore a(3)=24.

MAPLE

proc(n::nonnegint) local f, a; if n=0 or n=1 then return 1; end if; f:=L->[seq(add(L[i], i=2*nops(L)/3+1..j), j=2*nops(L)/3+1..nops(L))]; a:=f([seq(1, j=1..3^n)]); while nops(a)>3 do a:=f(a) end do; a[3]; end proc;

CROSSREFS

Cf. A107354, A109056, A109057, A109058, A109059, A109060, A109061, A109062.

Cf. A115728, A115729.

Sequence in context: A194157 A166736 A330297 * A318766 A292813 A293249

Adjacent sequences:  A109052 A109053 A109054 * A109056 A109057 A109058

KEYWORD

nonn

AUTHOR

Augustine O. Munagi, Jun 17 2005

EXTENSIONS

More terms from Paul D. Hanna (pauldhannaATjuno.com)

STATUS

approved

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Last modified September 26 03:46 EDT 2020. Contains 337346 sequences. (Running on oeis4.)