A102770 (p*q - 1)/2 where p and q are consecutive odd primes.

7, 17, 38, 71, 110, 161, 218, 333, 449, 573, 758, 881, 1010, 1245, 1563, 1799, 2043, 2378, 2591, 2883, 3278, 3693, 4316, 4898, 5201, 5510, 5831, 6158, 7175, 8318, 8973, 9521, 10355, 11249, 11853, 12795, 13610, 14445, 15483, 16199, 17285, 18431, 19010

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

Cf. A006094, A023515, A086870, A120876.

Sequence in context: A172156 A273947 A140121 * A253663 A298369 A213789

Adjacent sequences: A102767 A102768 A102769 * A102771 A102772 A102773

Keyword

easy,nonn

Author

W. Neville Holmes, Feb 10 2005

Status

approved