A097440 - OEIS

%I #10 Jul 17 2021 11:21:12

%S 25,11,5,7,27,17,1,53,105,175,39,15,15,25,149,35,117,119,317,65,123,

%T 43,187,173,119,1397,439,313,17,429,403,675,395,1491,135,1427,801,87,

%U 169,481,753,319,133,73,133,89,275,1155,1665,157,217,3121,279,2485,305

%N 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.

%e 25*2/2 = 25, 23 and 29 are consecutive primes so a(1) = 25.

%e 11*2*3/2 = 33, 31 and 37 are consecutive primes so a(2) = 11.

%t 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 *)

%Y Cf. A002110.

%Y Cf. A097439, A097441, A097570, A098064.

%K nonn

%O 1,1

%A _Pierre CAMI_, Aug 22 2004