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A108784 Difference between A107757 and A107755. 3
1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1, 1, 1, -1, 1, -1, -1, 1, -1, 1, 1, -1, -1, 1, 1, -1, 1, -1, -1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Of the 255 terms less than 10^4, 128 are positive.

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..120

FORMULA

It appears that a(n) = A076826(2n)-1. - T. D. Noe, Jun 14 2007

a(n) = A107757(n) - A107755(n).

MAPLE

Maple code from R. J. Mathar, Feb 25 2008:

A000108 := proc(n) option remember ; binomial(2*n, n)/(n+1) ; end:

A107757 := proc(n) option remember ; local a; if n = 1 then 3; else for a from A107757(n-1)+1 do if add(A000108(k), k=1..a) mod 3 = 2 then RETURN(a) ; fi ; od: fi ; end:

A107755 := proc(n) option remember ; local a; if n = 1 then 2; else for a from A107755(n-1)+1 do if add(A000108(k), k=1..a) mod 3 = 0 then RETURN(a) ; fi ; od: fi ; end:

A108784 := proc(n) A107757(n)-A107755(n) ; end: seq(A108784(n), n=1..120) ;

MATHEMATICA

s0 = s2 = {}; s = 0; Do[s = Mod[s + (2 n)!/n!/(n + 1)!, 3]; Switch[ Mod[s, 3], 0, AppendTo[s0, n], 2, AppendTo[s2, n]], {n, 10^4}]; s2 - s0

CROSSREFS

Cf. A107755, A107756, A107757.

Sequence in context: A119664 A257075 A010555 * A244513 A020985 A034947

Adjacent sequences:  A108781 A108782 A108783 * A108785 A108786 A108787

KEYWORD

sign

AUTHOR

Robert G. Wilson v, Jun 14 2005

EXTENSIONS

Corrected by T. D. Noe, Jun 14 2007

STATUS

approved

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Last modified June 17 15:07 EDT 2019. Contains 324185 sequences. (Running on oeis4.)