A116883 A number k is included iff (highest odd divisor of k)^2 >= k.

1, 3, 5, 6, 7, 9, 10, 11, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29, 30, 31, 33, 34, 35, 36, 37, 38, 39, 41, 42, 43, 44, 45, 46, 47, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 81, 82, 83

Offset

1,2

Comments

Also k is included if (and only if) the highest power of 2 dividing k is <= the largest odd divisor of k.

Links

Table of n, a(n) for n=1..71.

Example

20 = 4 * 5, where 4 is highest power of 2 dividing 20 and 5 is the largest odd number dividing 20. 4 is <= 5 (and, not coincidentally, 5^2 >= 20), so 20 is in the sequence.

Maple

isA116883 := proc(n) local dvs, hod, i ; dvs := convert(numtheory[divisors](n), list) ; for i from 1 to nops(dvs) do hod := op(-i, dvs) ; if hod mod 2 = 1 then RETURN(hod^2 >= n) ; fi ; od ; end: for n from 1 to 200 do if isA116883(n) then printf("%d, ", n) ; fi ; od ; # R. J. Mathar, May 10 2007

Mathematica

Select[Range[100], Last[Select[Divisors[#], OddQ]]^2>=#&] (* Harvey P. Dale, Nov 10 2013 *)
Select[Range[100], # >= 4^IntegerExponent[#, 2] &] (* Amiram Eldar, Jun 11 2022 *)

Crossrefs

Cf. A116882, A000265, A006519.

Sequence in context: A182834 A336426 A336497 * A256543 A186145 A364058

Adjacent sequences: A116880 A116881 A116882 * A116884 A116885 A116886

Keyword

easy,nonn

Author

Leroy Quet, Feb 24 2006

Extensions

More terms from R. J. Mathar, May 10 2007

Status

approved