|
|
A187371
|
|
Least odd number k such that (k*2^n-1)*k*2^n-1 or (k*2^n-1)*k*2^n+1 or (k*2^n+1)*k*2^n-1 or (k*2^n+1)*k*2^n+1 is prime.
|
|
5
|
|
|
1, 1, 1, 1, 1, 1, 3, 3, 1, 1, 5, 5, 3, 9, 7, 1, 5, 1, 3, 19, 9, 11, 7, 1, 11, 1, 27, 25, 9, 11, 3, 1, 21, 19, 1, 19, 3, 1, 7, 9, 9, 3, 27, 5, 1, 5, 5, 7, 3, 1, 41, 1, 9, 17, 1, 11, 1, 27, 3, 105, 33, 15, 23, 29, 19, 43, 37, 15, 3, 11, 27, 9, 57, 5, 3, 3, 35
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,7
|
|
COMMENTS
|
As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 0.24
|
|
LINKS
|
|
|
FORMULA
|
|
|
MATHEMATICA
|
Table[k = 1; While[! PrimeQ[(k*2^n - 1)*k*2^n - 1] && ! PrimeQ[(k*2^n - 1)*k*2^n + 1] && ! PrimeQ[(k*2^n + 1)*k*2^n - 1] && ! PrimeQ[(k*2^n + 1)*k*2^n + 1], k = k + 2]; k, {n, 100}]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|