trigamma(x) = d2(ln(factorial(n-1)))/dx2

# R program to find second derivative 
# of the lgamma value
  
# Calling the trigamma() Function
trigamma(2)
trigamma(4)
trigamma(5.2)

[1] 0.6449341
[1] 0.283823
[1] 0.2119756

# R program to find second derivative 
# of the lgamma value
  
# Creating a vector
x <- c(2.3, 3, 1.2)
  
# Calling the trigamma() Function
trigamma(x)
  
# Calling trigamma() function
# on negative values
trigamma(-2.3)
trigamma(-2)

[1] 0.5425375 0.3949341 1.2673772
[1] 14.72591
[1] Inf