OFFSET
1,1
COMMENTS
Written in binary, these numbers have exactly three 1 bits and the other bits are all 0's. This means that these numbers are of the sum of 1 plus two larger distinct powers of 2. - Alonso del Arte, Jul 08 2011
a(n) > A002110(n). [Reinhard Zumkeller, Jul 09 2011]
Sequence is not monotone: a(12) > a(13). [Charles R Greathouse IV, Jul 11 2011]
LINKS
Charles R Greathouse IV, Table of n, a(n) for n = 1..14
MATHEMATICA
list = {7}; For[max = 1; n = 2, n < 120,
For[m = 0, m < n,
tal = 2*(2^n + 2^m) + 1; num = PrimeNu[tal];
If[num > max, AppendTo[list, tal]; max = num]
, m++], n++] (* Sarnbratt *)
A084468 = Flatten[Table[2^m + 2^n + 1, {m, 2, 80}, {n, m - 1}]]; Flatten[Table[Take[Select[A084468, PrimeNu[#] == n &], 1], {n, 10}]] (* Alonso del Arte, Jul 08 2011 *)
PROG
(PARI) a(n)={
my(t);
for(a=2, 9e9,
t=1+1<<a;
for(b=1, a-1,
if(omega(t+1<<b)==n, return(t+1<<b))
)
)
}; \\ Charles R Greathouse IV, Jul 08 2011
(Haskell)
a192734 n = head [x | x <- [2^u + 2^v + 1 | u <- [2..], v <- [1..u-1]],
a001221 x == n]
-- Reinhard Zumkeller, Jun 14 2015, Jul 09 2011
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Johan Särnbratt, Jul 08 2011
EXTENSIONS
a(9) corrected by Charles R Greathouse IV, Jul 08 2011
a(12) from Charles R Greathouse IV, Jul 11 2011
STATUS
approved