# Specify the sample occurences (x), the sample size (n), and the null-hypothesis claim (p)
x <- 10
n <- 40
p <- 0.20
# P-value from right-tail proportion test at 0.05 significance level
prop.test(x, n, p, alternative = c("greater"), conf.level = 0.95, correct = FALSE)$p.value
[1] 0.2145977