A300912 Numbers of the form prime(x)*prime(y) where x and y are relatively prime.
4, 6, 10, 14, 15, 22, 26, 33, 34, 35, 38, 46, 51, 55, 58, 62, 69, 74, 77, 82, 85, 86, 93, 94, 95, 106, 118, 119, 122, 123, 134, 141, 142, 143, 145, 146, 155, 158, 161, 166, 177, 178, 187, 194, 201, 202, 205, 206, 209, 214, 215, 217, 218, 219, 221, 226, 249
Offset: 1
Keywords
Examples
The sequence of all relatively prime pairs (columns) begins: 1 1 1 1 2 1 1 2 1 3 1 1 2 3 1 1 2 1 4 1 3 1 2 1 3 1 2 3 4 3 5 6 5 7 4 8 9 7 5 10 11 9 12 5 13 7 14 11 15 8
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[100],And[PrimeOmega[#]==2,GCD@@PrimePi/@If[#==1,{},FactorInteger[#]][[All,1]]==1]&] With[{nn=40},Join[{4},Take[Prime[#[[1]]]Prime[#[[2]]]&/@Select[Subsets[ Range[ nn],{2}],CoprimeQ@@#&]//Union,Floor[Prime[nn]/2]]]] (* Harvey P. Dale, Jan 04 2021 *) -
PARI
ok(n)={my(f=factor(n)); bigomega(f)==2 && gcd(apply(primepi, f[,1]))==1} \\ Andrew Howroyd, Oct 26 2018