login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A138191 Denominator of (n-1)n(n+1)/12. 4
1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Proof of 4-periodicity follows from evaluating (n+3)(n+4)(n+5)/12, subtracting (n-1)n(n+1)/12 and getting n^2+4n+5 which is an integer. - R. J. Mathar, Mar 07 2008

LINKS

Table of n, a(n) for n=1..105.

Eric Weisstein's World of Mathematics, KirchhoffIndex

FORMULA

From R. J. Mathar, Mar 07 2008: (Start)

a(n) = 1 + (A000292(n-1) mod 2) = a(n-4).

O.g.f.: -1-5/(4(x-1))+1/(4(x+1))-1/(2(x^2+1)). (End)

a(n) = (1/24)*(5*(n mod 4) + 5*((n+1) mod 4) + 11*((n+2) mod 4) - ((n+3) mod 4)), with n>=0. - Paolo P. Lava, Mar 20 2008

EXAMPLE

0, 1/2, 2, 5, 10, 35/2, 28, 42, 60, 165/2, 110, 143, 182, ...

MATHEMATICA

Table[(n^3-n)/12, {n, 120}]//Denominator (* or *) PadRight[{}, 120, {1, 2, 1, 1}] (* Harvey P. Dale, Apr 15 2019 *)

CROSSREFS

Cf. A107453, A107453, A138190.

Sequence in context: A164115 A164117 A177704 * A069291 A268238 A081117

Adjacent sequences:  A138188 A138189 A138190 * A138192 A138193 A138194

KEYWORD

nonn,frac,mult

AUTHOR

Eric W. Weisstein, Mar 04 2008

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 12 04:27 EDT 2021. Contains 343810 sequences. (Running on oeis4.)