OFFSET
1,1
COMMENTS
Primes in this sequence: 7, 17, 71, 449, 881, 2591, ... - Zak Seidov, Jan 14 2013
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = (prime(n + 1)*prime(n + 2) - 1)/2.
a(n) ~ 0.5 n^2/log^2 n. - Charles R Greathouse IV, Jan 14 2013
a(n) = A023515(n+2)/2. - Jason Kimberley, Oct 23 2015
EXAMPLE
a(1) = (3*5 - 1)/2 = 7.
a(2) = (5*7 - 1)/2 = 17.
a(3) = (7*11 - 1)/2 = 38.
MATHEMATICA
Table[(Prime[n] Prime[n + 1] - 1)/2, {n, 2, 50}] (* Alonso del Arte, Jan 14 2013 *)
(Times@@#-1)/2&/@Partition[Prime[Range[2, 50]], 2, 1] (* Harvey P. Dale, Apr 10 2015 *)
PROG
(PARI) a(n)=prime(n+1)*prime(n+2)\2 \\ Charles R Greathouse IV, Jan 14 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
W. Neville Holmes, Feb 10 2005
STATUS
approved