OFFSET
1,1
COMMENTS
a(n) + 1 is an oblong number (A002378). - Michel Marcus, Feb 04 2017
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
20*20 + 20 - 1 = 419, 419 and 421 twin primes, 419 is the 7th of the sequence for k = 20.
MATHEMATICA
Select[Table[k(k+1)-1, {k, 500}], AllTrue[#+{0, 2}, PrimeQ]&] (* Harvey P. Dale, Jul 08 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Nov 09 2003
EXTENSIONS
Sign in definition corrected by R. J. Mathar, Nov 13 2009
STATUS
approved