21
by Dyke
Published 2001
22
by Andreescu
Published 2006
23
by Soifer
Published 2009
24
Published 2008
25
by Patterson
Published 2007
26
by Tan
Published 2009
27
by Romanes
Published 1986
28
by Weir
Published 2003
29
30
by Connolly
Published 2010
31
Published 2006
32
by Simpson
Published 2006
33
by Graves
Published 2007
34
by Rayner
Published 2009
35
by Seeley
Published 2008
36
by Quinn
Published 2002
37
by Sestoft
Published 2005
38
by Hardy, G. H.
Published 1921
39
by Deitel
Published 2010
40
by Dr K
Published 2004