The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A172398 Number of partitions of n into the sum of two refactorable numbers (A033950). 5
 0, 1, 1, 1, 0, 0, 0, 0, 1, 2, 1, 0, 1, 1, 0, 1, 1, 1, 1, 2, 1, 0, 0, 1, 1, 2, 1, 0, 0, 1, 0, 1, 1, 0, 0, 2, 1, 1, 0, 0, 1, 2, 0, 1, 1, 0, 0, 3, 1, 0, 0, 1, 0, 1, 0, 0, 1, 2, 0, 1, 1, 1, 0, 2, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,10 LINKS R. J. Mathar, Table of n, a(n) for n = 1..1000 FORMULA a(n) = Sum_{i=1..floor(n/2)} ((1+floor(i/d(i)) - ceiling(i/d(i))) * (1 + floor((n-i)/d(n-i)) - ceiling((n-i)/d(n-i)))). - Wesley Ivan Hurt, Jan 12 2013 EXAMPLE a(10)=2 because 10 = 1(refactorable) + 9(refactorable) = 2(refactorable) + 8(refactorable). MAPLE with(numtheory); a:=n-> sum( ((1 + floor(i/tau(i)) - ceil(i/tau(i))) * (1 + floor((n-i)/tau(n-i)) - ceil((n-i)/tau(n-i))) ), i=1..floor(n/2)); # alternative isA033950 := proc(n) if modp(n, numtheory[tau](n)) = 0 then true; else false; end if; end proc: A172398 := proc(n) local a; a := 0 ; for i from 1 to n/2 do if isA033950(i) and isA033950(n-i) then a := a+1 ; end if; end do: a ; end proc: # R. J. Mathar, Jul 21 2015 MATHEMATICA a[n_] := IntegerPartitions[n, {2}, Select[Range[n], Divisible[#, DivisorSigma[0, #]]&]] // Length; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Jun 04 2023 *) CROSSREFS Cf. A033950. Sequence in context: A099200 A358351 A093578 * A070107 A299908 A044933 Adjacent sequences: A172395 A172396 A172397 * A172399 A172400 A172401 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Nov 20 2010 EXTENSIONS Corrected by D. S. McNeil, Nov 20 2010 STATUS approved

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

Last modified February 23 02:31 EST 2024. Contains 370265 sequences. (Running on oeis4.)