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A161818 If b(n) = the largest proper divisor of n, then a(n) = (2^n - 1)/(2^b(n) - 1). 1
3, 7, 5, 31, 9, 127, 17, 73, 33, 2047, 65, 8191, 129, 1057, 257, 131071, 513, 524287, 1025, 16513, 2049, 8388607, 4097, 1082401, 8193, 262657, 16385, 536870911, 32769, 2147483647, 65537, 4196353, 131073, 270549121, 262145, 137438953471, 524289 (list; graph; refs; listen; history; text; internal format)
OFFSET
2,1
LINKS
EXAMPLE
a(6) = (2^6 - 1)/(2^3 - 1) = 63/7 = 9. - _Emeric Deutsch_, Jun 26 2009
MAPLE
with(numtheory): a := proc (n) options operator, arrow: (2^n-1)/(2^divisors(n)[tau(n)-1]-1) end proc: seq(a(n), n = 2 .. 40); # _Emeric Deutsch_, Jun 26 2009
MATHEMATICA
b[n_] := Divisors[n][[-2]];
a[n_] := (2^n - 1)/(2^b[n] - 1);
a /@ Range[2, 40] (* _Jean-François Alcover_, Nov 20 2020 *)
PROG
(PARI) a(n) = my(d=divisors(n)); (2^n-1)/(2^d[#d-1]-1); \\ _Michel Marcus_, Nov 20 2020
CROSSREFS
Cf. A032742.
Sequence in context: A048857 A005420 A212953 * A161509 A108974 A106853
KEYWORD
nonn
AUTHOR
_Leroy Quet_, Jun 20 2009
EXTENSIONS
Extended by _Emeric Deutsch_, Jun 26 2009
STATUS
approved

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Last modified March 3 03:04 EST 2024. Contains 370499 sequences. (Running on oeis4.)