This site is supported by donations to The OEIS Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A255891 Numbers n such that the sum of the even divisors of n is equal to m! and the sum of the odd divisors of n is equal to k! for some integers m and k. 1
 2, 4, 240, 348, 368, 380, 19364665320, 20210069880, 20328267960, 20673770040, 20681420760, 20735165880, 20940748920, 20959618680, 21135474360, 21196014840, 21256222680, 21302746920, 21380630040, 21405023640, 21426252120, 21465896760, 21522002040, 21544621560 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that A000593(n) = m! and A146076(n) = k! for some m and k. Is this sequence finite? No further terms less than 10^6. No further terms less than 10^9. - Michel Marcus, Mar 10 2015 sigma(a(25711)) >= 29! + 30!. - Hiroaki Yamanouchi, Mar 26 2015 LINKS Hiroaki Yamanouchi, Table of n, a(n) for n = 1..25710 EXAMPLE 240 is in the sequence because A000593(240)= 24 = 4! and A146076(240)= 720 = 6! MAPLE for n from 2 by 2  to 20000 do:    y:=divisors(n):n1:=nops(y):s0:=0:s1:=0:      for k from 1 to n1 do:        if irem(y[k], 2)=0         then         s0:=s0+ y[k]:         else         s1:=s1+ y[k]:       fi:      od:      ii:=0:         for a from 1 to 20 while(ii=0)do:          if s0=a!           then            for b from 1 to 20 while(ii=0) do:              if s1=b!               then               ii:=1:print(n):               else              fi:            od:           fi:         od:       od: MATHEMATICA fQ[n_] := Block[{d = Divisors@ n, lst = Array[Factorial, {449}]}, MemberQ[lst, Plus @@ Select[d, EvenQ]] && MemberQ[lst, Plus @@ Select[d, OddQ]]]; Select[Range@10000, fQ] (* Michael De Vlieger, Mar 10 2015 *) PROG (PARI) isoks(s) = {if (s==1, return (1)); f = 1; for (k=2, s, f *= k; if (f == s, return (1)); if (f > s, return (0)); ); } isok(n) = my(sod = sumdiv(n, d, d*(d%2))); my(sed = sigma(n) - sod); sod && sed && isoks(sed) && isoks(sod); \\ Michel Marcus, Mar 10 2015 CROSSREFS Cf. A000593, A146076, A245015. Sequence in context: A018729 A009800 A018742 * A018747 A110067 A145996 Adjacent sequences:  A255888 A255889 A255890 * A255892 A255893 A255894 KEYWORD nonn AUTHOR Michel Lagneau, Mar 09 2015 EXTENSIONS a(7)-a(24) from Hiroaki Yamanouchi, Mar 26 2015 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.

Last modified January 18 16:40 EST 2019. Contains 319271 sequences. (Running on oeis4.)