login
A234501
Products p*q*r*s of distinct primes for which (p*q*r*s + 1)/2 is prime.
3
1365, 3045, 4305, 4485, 4785, 4845, 5005, 5313, 6045, 6405, 7161, 7665, 8265, 8745, 9165, 9345, 9933, 10005, 10101, 10465, 10545, 10605, 10965, 11305, 11685, 12441, 12597, 13585, 14385, 14421, 14973, 15045, 15405, 15645, 15873, 16185, 16485, 17085, 17385
OFFSET
1,1
EXAMPLE
1365 = 3*5*7*13, and (1365+1)/2 = 683, a prime.
MATHEMATICA
t = Select[Range[1, 20000, 2], Map[Last, FactorInteger[#]] == Table[1, {4}] &]; Take[(t + 1)/2, 120] (* A234500*)
v = Flatten[Position[PrimeQ[(t + 1)/2], True]] ; w = Table[t[[v[[n]]]], {n, 1, Length[v]}] (* A234501 *)
(w + 1)/2 (* A234502 *) (* Peter J. C. Moses, Dec 23 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Clark Kimberling, Jan 01 2014
STATUS
approved