Special neighbor primes: Difference between revisions
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→{{header|Julia}}: stretching
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<lang julia>using Primes
function specialneighbors(N, savepairs=true)
neighbors, p1, pcount = Pair{Int}[], 2, 0
while (p2 = nextprime(p1 + 1)) < N
if isprime(p2 + p1 - 1
savepairs && push!(neighbors, p1 => p2)
pcount += 1
end
p1 = p2
end
return neighbors, pcount
end
spn, n = specialneighbors(100)
println("$n special neighbor prime pairs under 100:")
println("p1 p2 p1 + p2 - 1\n--------------------------")
for (p1, p2) in specialneighbors(100)[1]
println(lpad(p1, 2), " ", rpad(p2, 7), p1 + p2 - 1)
end
print("\nCount of such prime pairs under 1,000,000,000: ",
specialneighbors(1_000_000_000, false)[2])
</lang>{{out}}
<pre>
13 special neighbor prime pairs under 100:
p1 p2 p1 + p2 - 1
--------------------------
Line 167 ⟶ 174:
67 71 137
73 79 151
Count of such prime pairs under 1,000,000,000: 6041231
</pre>
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