OFFSET
1,1
COMMENTS
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Christian Krause, LODA program for A084921
FORMULA
a(n) = A084920(n)/2 for n > 1.
a(n) = 3*A084922(n) for n > 2.
a(n) ~ 0.5 n^2 log^2 n. - Charles R Greathouse IV, May 15 2013
Product_{n>=1} (1 + 1/a(n)) = 2. - Amiram Eldar, Jan 23 2021
a(n) = (A000040(n)^2 - 1) / 2 for n > 1. - Christian Krause, Mar 27 2021
a(n) = (3/2)*A024700(n-2), for n > 1. - G. C. Greubel, May 03 2024
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
(Magma) [3] cat [(p^2-1)/2: p in PrimesInInterval(3, 300)]; // G. C. Greubel, May 03 2024
(SageMath) [3]+[(n^2-1)/2 for n in prime_range(3, 301)] # G. C. Greubel, May 03 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 11 2003
STATUS
approved