login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A084921 a(n) = lcm(p-1, p+1) where p is the n-th prime. 15
3, 4, 12, 24, 60, 84, 144, 180, 264, 420, 480, 684, 840, 924, 1104, 1404, 1740, 1860, 2244, 2520, 2664, 3120, 3444, 3960, 4704, 5100, 5304, 5724, 5940, 6384, 8064, 8580, 9384, 9660, 11100, 11400, 12324, 13284, 13944, 14964, 16020, 16380 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

This sequence consists of terms of sequences A055523 and A055527 for prime n > 2. - Toni Lassila (tlassila(AT)cc.hut.fi), Feb 02 2004

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Index entries for sequences related to lcm's

FORMULA

a(n) = A084920(n)/2 for n > 1; a(n) = A084922(n)*3 for n > 2.

a(n) = A009286(A000040(n)). - Enrique Pérez Herrero, May 17 2012

a(n) ~ 0.5 n^2 log^2 n. - Charles R Greathouse IV, May 15 2013

MATHEMATICA

LCM[#-1, #+1]&/@Prime[Range[50]] (* Harvey P. Dale, Oct 09 2018 *)

PROG

(PARI) a(n)=if(n<2, 3, (prime(n)^2-1)/2) \\ Charles R Greathouse IV, May 15 2013

(Haskell)

a084921 n = lcm (p - 1) (p + 1)  where p = a000040 n

-- Reinhard Zumkeller, Jun 01 2013

CROSSREFS

Cf. A000040, A006093, A008864, A055523, A055527.

Sequence in context: A081621 A073713 A291023 * A070765 A000577 A111758

Adjacent sequences:  A084918 A084919 A084920 * A084922 A084923 A084924

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jun 11 2003

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 December 10 14:27 EST 2019. Contains 329896 sequences. (Running on oeis4.)