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A187370
Least odd number k such that (k*2^n+1)*k*2^n + 1 is prime.
5
1, 3, 1, 5, 9, 3, 21, 3, 1, 11, 13, 5, 27, 27, 7, 5, 27, 3, 27, 41, 13, 11, 49, 5, 69, 83, 61, 47, 9, 21, 3, 3, 45, 35, 21, 21, 3, 3, 7, 39, 9, 3, 27, 51, 73, 35, 27, 33, 27, 125, 103, 255, 27, 63, 207, 171, 153, 27, 3, 105, 147
OFFSET
1,2
COMMENTS
As N increases, it appears that (sum_{k=1..N} a(k)) / (sum_{k=1..N} k) tends to 1.25.
MATHEMATICA
Table[k = 1; While[! PrimeQ[(k*2^n + 1)*k*2^n + 1], k = k + 2]; k, {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Mar 09 2011
STATUS
approved