A097440 Least k such that k*prime(n)#/2 - 2 and k*prime(n)#/2 + 4 are consecutive primes, where prime(n)# is the n-th primorial.

25, 11, 5, 7, 27, 17, 1, 53, 105, 175, 39, 15, 15, 25, 149, 35, 117, 119, 317, 65, 123, 43, 187, 173, 119, 1397, 439, 313, 17, 429, 403, 675, 395, 1491, 135, 1427, 801, 87, 169, 481, 753, 319, 133, 73, 133, 89, 275, 1155, 1665, 157, 217, 3121, 279, 2485, 305

Offset

1,1

Links

Table of n, a(n) for n=1..55.

Example

25*2/2 = 25, 23 and 29 are consecutive primes so a(1) = 25.
11*2*3/2 = 33, 31 and 37 are consecutive primes so a(2) = 11.

Mathematica

a[n_] := Module[{k = 1, p = Product[Prime[i], {i, 1, n}]}, While[!(PrimeQ[k*p/2-2] && NextPrime[k*p/2-2] == k*p/2+4), k++]; k]; Array[a, 55] (* Amiram Eldar, Jul 17 2021 *)

Crossrefs

Cf. A002110.

Cf. A097439, A097441, A097570, A098064.

Sequence in context: A217432 A040604 A358131 * A040603 A033345 A241309

Adjacent sequences: A097437 A097438 A097439 * A097441 A097442 A097443

Keyword

nonn

Author

Pierre CAMI, Aug 22 2004

Status

approved