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!)
A141550 Numbers n whose deficiency is 14. 7
27, 34, 232, 34432, 549762629632 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(6) > 10^12. - Donovan Johnson, Dec 08 2011

a(6) > 10^13. - Giovanni Resta, Mar 29 2013

a(6) > 10^18. - Hiroaki Yamanouchi, Aug 21 2018

a(6) <= b(38) = 37778931864743868104704 = 3.77789*10^22, since b(k) = 2^(k-1)*(2^k+13) is in this sequence for all k in A102634, i.e., 2^k+13 is prime. All known terms except a(1) = 27 are of this form: a(2..5) = b(k) with k = 2, 4, 8, 20, and k = 38 yields the next larger term of this form. - M. F. Hasler, Jul 18 2016

Any term x of this sequence can be combined with any term y of A141546 to satisfy the property (sigma(x)+sigma(y))/(x+y) = 2, which is a necessary (but not sufficient) condition for two numbers to be amicable. - Timothy L. Tiffin, Sep 13 2016

LINKS

Table of n, a(n) for n=1..5.

EXAMPLE

a(1) = 27, since 2*27 - sigma(27) = 54 - 40 = 14. - Timothy L. Tiffin, Sep 13 2016

MATHEMATICA

lst={}; Do[If[n==Plus@@Divisors[n]-n+14, AppendTo[lst, n]], {n, 10^4}]; Print[lst];

Select[Range[1, 10^8], DivisorSigma[1, #] - 2 # == - 14 &] (* Vincenzo Librandi, Sep 14 2016 *)

PROG

(MAGMA) [n: n in [1..9*10^6] | (SumOfDivisors(n)-2*n) eq -14]; // Vincenzo Librandi, Sep 14 2016

CROSSREFS

Cf. A000203, A033880, A005100; A191363 (deficiency 2), A125246 (deficiency 4), A141548 (deficiency 6), A125247 (deficiency 8), A101223 (deficiency 10), A141549 (deficiency 12), A125248 (deficiency 16); A141546 (abundance 14).

Sequence in context: A309063 A088499 A058902 * A032584 A072492 A164376

Adjacent sequences:  A141547 A141548 A141549 * A141551 A141552 A141553

KEYWORD

nonn

AUTHOR

Vladimir Joseph Stephan Orlovsky, Aug 16 2008

EXTENSIONS

a(5) from Donovan Johnson, Dec 08 2011

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 August 13 02:09 EDT 2020. Contains 336441 sequences. (Running on oeis4.)