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A090076 a(n) = prime(n)*prime(n+2). 18
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A192133. - Reinhard Zumkeller, Jun 26 2011

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

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

EXAMPLE

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

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 *)

PROG

(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

(Haskell)

a090076 n = a090076_list !! (n-1)

a090076_list = zipWith (*) a000040_list $ drop 2 a000040_list

-- Reinhard Zumkeller, Dec 17 2014

CROSSREFS

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

Cf. A078898.

Sequence in context: A042309 A215757 A048697 * A231966 A156592 A045973

Adjacent sequences:  A090073 A090074 A090075 * A090077 A090078 A090079

KEYWORD

easy,nonn

AUTHOR

Felix Tubiana (fat2(AT)columbia.edu), Jan 21 2004

EXTENSIONS

Extended by Robert G. Wilson v, Jan 22 2004

STATUS

approved

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Last modified May 8 19:28 EDT 2021. Contains 343666 sequences. (Running on oeis4.)