login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A274793 Numbers not in the range of the sum of odd divisors function. 2
2, 3, 5, 7, 9, 10, 11, 15, 16, 17, 19, 21, 22, 23, 25, 26, 27, 28, 29, 33, 34, 35, 36, 37, 39, 41, 43, 45, 46, 47, 49, 50, 51, 52, 53, 55, 58, 59, 61, 63, 64, 65, 66, 67, 69, 70, 71, 73, 75, 76, 77, 79, 81, 82, 83, 85, 86, 87, 88, 89, 91, 92, 93, 94, 95, 97, 99, 100 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers which do not appear in A000593; that is, there is no positive integer N whose sum of odd divisors is equal to a(n) for any n.

The sum of odd divisors of x is equal to sigma(x) if and only if x is odd.  So, there are numbers in the range of sigma(x) that are not in the range of the sum of odd divisors function.

LINKS

Table of n, a(n) for n=1..68.

MATHEMATICA

TakeWhile[Complement[Range@ #, Union@ Table[Total@ Select[Divisors@ n, OddQ], {n, 2 #}]], Function[k, k <= #]] &@ 100 (* Michael De Vlieger, Jul 07 2016 *)

CROSSREFS

Cf. A000593, supersequence of A007369, A274790 (complement).

Sequence in context: A167857 A117284 A137377 * A168543 A026277 A201804

Adjacent sequences:  A274790 A274791 A274792 * A274794 A274795 A274796

KEYWORD

nonn

AUTHOR

Timothy L. Tiffin, Jul 07 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 19 13:25 EST 2020. Contains 332044 sequences. (Running on oeis4.)