OFFSET
1,1
LINKS
Ray Chandler, Table of n, a(n) for n = 1..25
EXAMPLE
n = 8: a(8) = 19417793, phi(a(8)) = 19199380 = 2*9699690 = 2*2*3*5*7*11*13*17*19.
MATHEMATICA
nmax = 25;
A066676 = {};
pm = 1;
Do[
pm *= Prime[n];
sol = 0;
If[PrimeQ[pm + 1],
sol = pm + 1;
,
sd = Select[Divisors[pm/2], # <= Sqrt[pm/2] &];
Do[
f1 = sd[[i]];
f2 = pm/2/f1;
If[PrimeQ[2 f1 + 1] && PrimeQ[2 f2 + 1],
sol = (2 f1 + 1)*(2 f2 + 1);
Break[];
];
, {i, Length[sd], 1, -1}];
];
AppendTo[A066676, sol];
Print[{n, sol}];
, {n, nmax}];
A066676 (* Ray Chandler, Oct 21 2011 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Dec 19 2001
EXTENSIONS
a(9)-a(11) from Donovan Johnson, Oct 12 2011
a(12)-a(13) upper limits from Donovan Johnson confirmed as next terms, a(14)-a(19) added by Ray Chandler, Oct 21 2011
STATUS
approved