This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A278933 Number of 2 X 2 matrices with entries in {0,1,...,n} and permanent = trace with no entry repeated. 2
 0, 0, 0, 0, 0, 0, 4, 4, 8, 8, 12, 12, 20, 20, 24, 28, 32, 32, 40, 40, 48, 52, 56, 56, 68, 68, 72, 76, 84, 84, 96, 96, 104, 108, 112, 116, 128, 128, 132, 136, 148, 148, 160, 160, 168, 176, 180, 180, 196, 196, 204 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS a(n) mod 4 = 0. LINKS Indranil Ghosh and Chai Wah Wu, Table of n, a(n) for n = 0..10000 (terms for n = 0..285 from Indranil Ghosh) PROG (Python) def t(n):     s=0     for a in range(0, n+1):         for b in range(0, n+1):             for c in range(0, n+1):                 for d in range(0, n+1):                     if (a!=b  and a!=d and b!=d and c!=a and c!=b and c!=d):                         if (a*d+b*c)==a+d:                             s+=1     return s for i in range(0, 286):     print str(i)+" "+str(t(i)) CROSSREFS Cf. A210288 (wherein the entries can be repeated). Sequence in context: A071339 A146890 A168273 * A145447 A204989 A101921 Adjacent sequences:  A278930 A278931 A278932 * A278934 A278935 A278936 KEYWORD nonn AUTHOR Indranil Ghosh, Dec 02 2016 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 | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified October 17 16:18 EDT 2018. Contains 316285 sequences. (Running on oeis4.)