|
|
A162860
|
|
Numbers k such that k^2+4*k+1 is prime.
|
|
1
|
|
|
2, 6, 8, 12, 18, 24, 30, 32, 38, 42, 44, 56, 62, 66, 78, 84, 86, 90, 96, 108, 110, 116, 122, 126, 134, 138, 140, 144, 162, 170, 188, 192, 200, 204, 206, 216, 218, 248, 252, 264, 266, 294, 296, 302, 308, 318, 320, 324, 326, 330, 338, 348, 354, 360, 368, 414, 416
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
a(1) = k = 2 is in the sequence because 2^2+4*2+1=13 = A028874(1) is prime.
|
|
MATHEMATICA
|
f[a_]:=a^2+4*a+1; lst={}; Do[If[PrimeQ[f[n]], AppendTo[lst, n]], {n, 6!}]; lst
Select[Range[500], PrimeQ[#^2+4#+1]&] (* Harvey P. Dale, May 28 2012 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|