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N.B. A detailed on-line essay by S. Finch was the starting point for this entry.
Let 
 be the number of 1s in the Binary expression of 
.  Then the number of Odd Binomial
Coefficients 
 where 
 is 
 (Glaisher 1899, Fine 1947).  The
number of Odd elements in the first 
 rows of Pascal's Triangle is
![]()  | 
(1) | 
| (2) | 
| (3) | 
| (4) | 
References
Finch, S.  ``Favorite Mathematical Constants.''  http://www.mathsoft.com/asolve/constant/stlrsky/stlrsky.html
 
Fine, N. J.  ``Binomial Coefficients Modulo a Prime.''  Amer. Math. Monthly 54, 589-592, 1947.
 
Wolfram, S.  ``Geometry of Binomial Coefficients.''  Amer. Math. Monthly 91, 566-571, 1984.