Duffinian numbers: Difference between revisions
→{{header|Julia}}
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;* [[oeis:A003624|OEIS:A003624 - Duffinian numbers: composite numbers k relatively prime to sigma(k)]]
=={{header|Julia}}==
<lang julia>using Primes
function σ(n)
f = [one(n)]
for (p,e) in factor(n)
f = reduce(vcat, [f*p^j for j in 1:e], init=f)
end
return sum(f)
end
isDuffinian(n) = !isprime(n) && gcd(n, σ(n)) == 1
function testDuffinians()
println("First 50 Duffinian numbers:")
foreach(p -> print(rpad(p[2], 4), p[1] % 25 == 0 ? "\n" : ""),
enumerate(filter(isDuffinian, 2:217)))
n, found = 2, 0
println("\nFifteen Duffinian triplets:")
while found < 15
if isDuffinian(n) && isDuffinian(n + 1) && isDuffinian(n + 2)
println(lpad(n, 6), lpad(n +1, 6), lpad(n + 2, 6))
found += 1
end
n += 1
end
end
testDuffinians()
</lang>{{out}}
<pre>
First 50 Duffinian numbers:
4 8 9 16 21 25 27 32 35 36 39 49 50 55 57 63 64 65 75 77 81 85 93 98 100
111 115 119 121 125 128 129 133 143 144 155 161 169 171 175 183 185 187 189 201 203 205 209 215 217
Fifteen Duffinian triplets:
63 64 65
323 324 325
511 512 513
721 722 723
899 900 901
1443 1444 1445
2303 2304 2305
2449 2450 2451
3599 3600 3601
3871 3872 3873
5183 5184 5185
5617 5618 5619
6049 6050 6051
6399 6400 6401
8449 8450 8451
</pre>
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