%I #5 Apr 03 2023 10:36:10

%S 2,2,4,6,120,120,120,21972720,827779590,2481129210,3894254360010

%N Smallest k such that k*prime(i)-1 is prime for i = 1 to n.

%C Perhaps a(10) = 2481129210 (from Prime Curios web page)

%C For n > 4, a(n) == 0 mod 30. a(10) was reported by a Prime Curios page.

%H Chris Caldwell, <a href="https://t5k.org/curios/">Prime Curios</a>

%e a(4) = 6, 2*6-1 = 11, 3*6-1 = 17, 5*6-1 = 29, 7*6-1 = 41 are all primes.

%t k = 2; Do[ While[ Union[ PrimeQ[ Table[ k*Prime[i] - 1, {i, 1, n}]]] != {True}, k+=2]; Print[k], {n, 1, 8}]

%Y Cf. A084700.

%K more,nonn

%O 1,1

%A _Amarnath Murthy_, Jun 08 2003

%E Edited and extended by _Robert G. Wilson v_ and _Don Reble_, Jun 15 2003