A061798 - OEIS

%I #34 May 14 2024 06:04:30

%S 0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,2,2,2,2,3,3,3,4,4,4,4,4,5,5,7,

%T 7,8,8,8,9,10,10,10,10,10,10,10,10,12,12,12,13,13,14,15,16,16,16,17,

%U 17,19,19,19,19,20,20,20,21,23,24,24,24,25,25,25,25

%N Number of sums i^3 + j^3 that occur more than once for 1<=i<=j<=n.

%H Seiichi Manyama, <a href="/A061798/b061798.txt">Table of n, a(n) for n = 1..1000</a>

%o (PARI) a(n) = my(v=vector(2*n^3, i, 0)); for(i=1, n, for(j=i, n, v[i^3+j^3]+=1)); sum(i=1, #v, v[i]>1); \\ _Seiichi Manyama_, May 14 2024

%o (Ruby)

%o def A(n)

%o   h = {}

%o   (1..n).each{|i|

%o     (i..n).each{|j|

%o       k = i * i * i + j * j * j

%o       if h.has_key?(k)

%o         h[k] += 1

%o       else

%o         h[k] = 1

%o       end

%o     }

%o   }

%o   h.to_a.select{|i| i[1] > 1}.size

%o end

%o def A061798(n)

%o   (1..n).map{|i| A(i)}

%o end

%o p A061798(80) # _Seiichi Manyama_, May 14 2024

%Y Cf. A000217, A011541, A061791.

%K nonn

%O 1,16

%A _Labos Elemer_, Jun 22 2001