A354266 - OEIS

%I #7 May 22 2022 05:33:46

%S 2,4,2,6,3,6,2,8,4,6,2,10,3,9,4,8,2,12,4,10,6,8,3,12,5,10,6,9,2,14,4,

%T 12,6,10,2,16,3,15,4,14,6,12,8,10,2,18,4,16,5,15,6,14,8,12,3,18,6,15,

%U 7,14,9,12,2,20,4,18,6,16,8,14,10,12,2,22,3,21

%N Pairs of integers (s, t) such that 0 < s < t and gcd(s, t) > 1, where the pairs are generated by the boustrophedonic Cantor enumeration A319571.

%e The sequence of pairs starts:

%e (2, 4), (2, 6), (3, 6), (2, 8), (4, 6), (2, 10), (3, 9), (4, 8), (2, 12), (4, 10),(6, 8), (3, 12), (5, 10), (6, 9), (2, 14), (4, 12), (6, 10), (2, 16), (3, 15),(4, 14), (6, 12), (8, 10), ...

%o (Julia)

%o function A354266List(upto)

%o     L = Int[]

%o     for n in 1:upto

%o         d = div(isqrt(8n + 1) - 1, 2)

%o         s = n - div(d*(d + 1), 2)

%o         t = d - s

%o         if s > 0 && s < t && gcd(s, t) > 1

%o             push!(L, s)

%o             push!(L, t)

%o         end

%o     end

%o L end

%o println(A354266List(303))

%Y Cf. A319571.

%K nonn

%O 1,1

%A _Peter Luschny_, May 21 2022