Math.gamma(x) รข float
Class Public methods
Calculates the gamma function of x.
Note that gamma(n) is same as fact(n-1) for integer n > 0. However gamma(n) returns float and can be an approximation.
def fact(n) (1..n).inject(1) {|r,i| r*i } end
1.upto(26) {|i| p [i, Math.gamma(i), fact(i-1)] }
#=> [1, 1.0, 1]
# [2, 1.0, 1]
# [3, 2.0, 2]
# [4, 6.0, 6]
# [5, 24.0, 24]
# [6, 120.0, 120]
# [7, 720.0, 720]
# [8, 5040.0, 5040]
# [9, 40320.0, 40320]
# [10, 362880.0, 362880]
# [11, 3628800.0, 3628800]
# [12, 39916800.0, 39916800]
# [13, 479001600.0, 479001600]
# [14, 6227020800.0, 6227020800]
# [15, 87178291200.0, 87178291200]
# [16, 1307674368000.0, 1307674368000]
# [17, 20922789888000.0, 20922789888000]
# [18, 355687428096000.0, 355687428096000]
# [19, 6.402373705728e+15, 6402373705728000]
# [20, 1.21645100408832e+17, 121645100408832000]
# [21, 2.43290200817664e+18, 2432902008176640000]
# [22, 5.109094217170944e+19, 51090942171709440000]
# [23, 1.1240007277776077e+21, 1124000727777607680000]
# [24, 2.5852016738885062e+22, 25852016738884976640000]
# [25, 6.204484017332391e+23, 620448401733239439360000]
# [26, 1.5511210043330954e+25, 15511210043330985984000000]
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