login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A239436 Members of a pair (m,n) such that sigma(m) = sigma(n) = sigma(m+n), m < n where sigma = A000203. 2
1288, 1485, 5775, 6128, 8008, 11685, 16744, 19305, 21896, 25245, 24472, 28215, 26488, 35505, 32620, 45441, 37352, 43065, 39928, 46035, 47656, 54945, 50260, 65637, 52808, 60885, 55384, 63855, 62744, 75495, 72772, 79365, 68264, 78705, 75075, 79664, 80584, 90915 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The numbers such that sigma(n) = sigma(m) = m+n+1 and m+n is prime are in the sequence since sigma(n+m) = m+n+1 (see A005276). - Giovanni Resta, Mar 20 2014

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..10000

EXAMPLE

The pair (1288, 1485) is in the sequence because sigma(1288) = sigma(1485) = 2880 and sigma(1288+1485) = sigma(2773) = 2880.

MATHEMATICA

a[n1_, n2_] := (t = Table[{DivisorSigma[1, n], n}, {n, n1, n2}] // Sort; s = Select[Split[t, #1[[1]] == #2[[1]] &], Length[#] >= 2 &]; f[lst_] := Select[Table[{lst[[i]], lst[[j]]}, {i, 1, Length[lst] - 1}, {j, i + 1, Length[lst]}] // Flatten[#, 1] &, #[[1, 1]] == DivisorSigma[1, #[[1, 2]] + #[[2, 2]]] &]; Select[f /@ s, # != {} &]); Flatten[a[1, 10^5], 2][[All, 2]] (* Jean-François Alcover, Mar 20 2014 *)

CROSSREFS

Cf. A000203, A005276.

Sequence in context: A104399 A232253 A140914 * A239939 A179573 A264243

Adjacent sequences:  A239433 A239434 A239435 * A239437 A239438 A239439

KEYWORD

nonn,hard

AUTHOR

Michel Lagneau, Mar 18 2014

EXTENSIONS

More terms from Jean-François Alcover, Mar 20 2014

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 October 19 03:34 EDT 2019. Contains 328211 sequences. (Running on oeis4.)