A097441 Least k such that k*prime(n)#/2 - 4 and k*prime(n)#/2 + 2 are consecutive primes, where prime(n)# is the n-th primorial.

27, 9, 9, 9, 7, 27, 7, 9, 19, 9, 21, 1, 267, 47, 1, 69, 307, 19, 585, 37, 147, 313, 159, 251, 99, 73, 355, 197, 225, 545, 99, 5, 481, 2359, 337, 285, 95, 993, 903, 279, 779, 123, 519, 1201, 1717, 1551, 261, 123, 1649, 1571, 87, 1325, 537, 201, 2131, 1403, 205, 863

Offset

1,1

Links

Table of n, a(n) for n=1..58.

Example

27*2/2 = 27, 23 and 29 are consecutive primes so a(1) = 27.
9*2*3/2 = 27 so a(2) = 9.

Mathematica

a[n_] := Module[{k = 1, p = Product[Prime[i], {i, 1, n}]}, While[!(PrimeQ[k*p/2-4] && NextPrime[k*p/2-4] == k*p/2+2), k++]; k]; Array[a, 60] (* Amiram Eldar, Jul 17 2021 *)

Crossrefs

Cf. A002110.

Cf. A097439, A097440, A097570, A098064.

Sequence in context: A040710 A040708 A214103 * A040707 A040706 A069893

Adjacent sequences: A097438 A097439 A097440 * A097442 A097443 A097444

Keyword

nonn

Author

Pierre CAMI, Aug 22 2004

Status

approved