How to get different result with repetition simulation?

I was trying to test a standard error of a randomly chosen sample of 24 chosen from 64 objects, but when I try to run it 10 times it gives 10 same answers. What is the right way to test it with repetition? This is my code and results.

po=c(900,822,781,805,670,1238,573,634,578,487,442,451,459,464,400,366,364,317,328,302,288,291,253,291,308,272,284,255,270,214,195,260,209,183,163,253,232,260,201,147,292,164,143,169,139,170,150,143,113,115,123,154,140,119,130,127,100,107,114,111,163,116,122,134)

se_1 = sd(sample(po[1:64],24,replace = FALSE)) * sqrt(1/24)

rep(se_1, times=10)
#[1] 44.69907 44.69907 44.69907 44.69907 44.69907 44.69907 44.69907 44.69907
#[9] 44.69907 44.69907