A090076 a(n) = prime(n)*prime(n+2).

10, 21, 55, 91, 187, 247, 391, 551, 713, 1073, 1271, 1591, 1927, 2279, 2773, 3233, 3953, 4331, 4891, 5609, 6059, 7031, 8051, 8989, 9991, 10807, 11227, 12091, 13843, 14803, 17399, 18209, 20413, 20989, 23393, 24613, 26219, 28199, 29893, 31313

Offset: 1

Author

Felix Tubiana, Jan 21 2004

Keywords

• easy
• nonn

Comments

Subsequence of A192133. - Reinhard Zumkeller, Jun 26 2011

For n > 1: A078898(a(n)) = 4. - Reinhard Zumkeller, Apr 06 2015

Examples

			a(5) = prime(5)*prime(7) = 11*17 = 187.
		

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• C. Cobeli and A. Zaharescu, A game with divisors and absolute differences of exponents, Journal of Difference Equations and Applications, Vol. 20, #11 (2014) pp. 1489-1501, DOI: 10.1080/10236198.2014.940337. Also available as arXiv:1411.1334 [math.NT], 2014.

Crossrefs

Subset of the squarefree semiprimes, A006881. Cf. A006094, A090090.

Cf. A078898.

Programs

Haskell

a090076 n = a090076_list !! (n-1)
a090076_list = zipWith (*) a000040_list $ drop 2 a000040_list
-- Reinhard Zumkeller, Dec 17 2014

Mathematica

Table[Prime[n] Prime[n + 2], {n, 1, 40}] (* Robert G. Wilson v, Jan 22 2004 *)
Last[#]First[#]&/@Partition[Prime[Range[50]],3,1] (* Harvey P. Dale, May 08 2013 *)

MuPAD

ithprime(i)*ithprime(i+2) $ i = 1..40 // Zerinvary Lajos, Feb 26 2007

Sage

def prime_gaps(n):
    primegaps = []
    nprimes = primes_first_n(n+1)
    for i in range(2, n+1):
        primegaps.append(nprimes[i]*nprimes[i-2])
    return primegaps
print(prime_gaps(60)) # Zerinvary Lajos, Jul 08 2008

Extensions

Extended by Robert G. Wilson v, Jan 22 2004