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A102770 (p*q - 1)/2 where p and q are consecutive odd primes. 4
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 18 11:24 EST 2019. Contains 319271 sequences. (Running on oeis4.)