OFFSET
1,2
COMMENTS
m is in the sequence if and only if the multiplicative order of 2 (mod 2m-1) is odd.
REFERENCES
R. K. Guy, Unsolved Problems in Number Theory, E38.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
P. Alles, On a Conjecture of J. Pelikan, J. Comb. Th. A 60 (1992) 312-313.
N. F. J. Inglis and J. D. A. Wiseman, Very odd sequences, J. Comb. Th. A 71 (1995) 89-96.
F. J. MacWilliams and A. M. Odlyzko, Pelikan's conjecture and cyclotomic cosets, J. Comb. Th. A 22 (1977) 110-114.
FORMULA
a(n) = (A036259(n) + 1)/2.
MATHEMATICA
o2[ m_ ] := Module[ {e, t}, For[ e = 1; t = 2, Mod[ t-1, m ] >0, e++, t = Mod[ 2t, m ] ]; e ]; Select[ Range[ 1, 500 ], OddQ[ o2[ 2#-1 ] ] & ]
(* Second program: *)
(Select[Range[1, 999, 2], OddQ[MultiplicativeOrder[2, #]]&] + 1)/2 (* Jean-François Alcover, Dec 20 2017 *)
PROG
(PARI) is(n)=znorder(Mod(2, 2*n-1))%2 \\ Charles R Greathouse IV, Jun 24 2015
(PARI) A000265(n)=n>>valuation(n, 2)
is(n)=Mod(2, 2*n-1)^A000265(eulerphi(2*n-1))==1 \\ Charles R Greathouse IV, Jun 24 2015
(Python)
from sympy import n_order
def A053006_gen(startvalue=1): # generator of terms >= startvalue
return filter(lambda n:n_order(2, (n<<1)-1)&1, count(max(startvalue, 1)))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms from John W. Layman, Feb 21 2000
Additional information from Dean Hickerson, May 25 2001
STATUS
approved