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!)
A274552 Numbers n such that sigma(n) == 0 (mod n-3). 2
4, 5, 6, 7, 8, 15, 52, 315, 592, 1155, 2102272, 815634435 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..12.

EXAMPLE

sigma(4) mod 4-3 = 7 mod 1 = 0.

MAPLE

with(numtheory); P:=proc(q, h) local n;  for n from 1 to q do

if n+h>0 then if type(sigma(n)/(n+h), integer) then print(n); fi; fi; od; end: P(10^9, -3);

MATHEMATICA

k = -3; Select[Range[Abs@ k + 1, 10^6], Mod[DivisorSigma[1, #], # + k] == 0 &] (* Michael De Vlieger, Jul 01 2016 *)

PROG

(MAGMA) [n: n in [4..2*10^6] | SumOfDivisors(n) mod (n-3) eq 0 ]; // Vincenzo Librandi, Jul 02 2016

(PARI) is(n) = if(n < 4, return(0), Mod(sigma(n), n-3)==0) \\ Felix Fröhlich, Jul 02 2016

CROSSREFS

Cf. A067702, A087485, A141548, A274551, A274553-A274566.

Sequence in context: A285218 A059709 A071623 * A280682 A140293 A075341

Adjacent sequences:  A274549 A274550 A274551 * A274553 A274554 A274555

KEYWORD

nonn,more

AUTHOR

Paolo P. Lava, Jun 28 2016

EXTENSIONS

a(11)-a(12) from Giovanni Resta

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 March 29 13:55 EDT 2020. Contains 333107 sequences. (Running on oeis4.)