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Neil Gunther has pointed out on his blog that the prime number decomposition R package schoolmath contains mistakes in the function primes, listing 1 as a prime number but also including decomposable numbers like 133 in its list of prime numbers:
> primes(100,140)
[1] 101 107 111 113 123 129 131 137
> primes(50,140)
[1] 51 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 133
[20] 137 139
> is.prim(primes(133)
[1] FALSE
> is.prim(primes(200,300))
[1] FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE FALSE TRUE
[13] TRUE TRUE TRUE TRUE TRUE TRUE
> sum(1-is.prim(primes(1,1000)))
[1] 10
> data(primlist)
> sum(1-is.prim(primlist[1:25000]))
[1] 3309
This is rather annoying and I hope it gets quickly fixed!
Filed under: R Tagged: bug, prime factor decomposition, prime numbers, R, schoolmath
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