cp's OEIS Frontend

A339389 a(n) is the number of ordered pairs (i, j) of numbers in the range 1..n-1 such that a(i) + a(j) >= a(n-1).

%I A339389 #14 Mar 04 2021 14:10:32
%S A339389 0,1,3,5,8,12,14,21,21,38,23,68,24,114,28,149,36,182,47,209,60,247,68,
%T A339389 315,70,397,68,515,71,605,82,667,106,690,147,700,206,717,255,747,282,
%U A339389 835,244,1103,160,1462,124,1751,131,1913,160,1990,213,1988,324,1771
%N A339389 a(n) is the number of ordered pairs (i, j) of numbers in the range 1..n-1 such that a(i) + a(j) >= a(n-1).
%C A339389 Graphically, we have two curves that correspond to the bisections (see illustration in Links section).
%H A339389 Rémy Sigrist, <a href="/A339389/b339389.txt">Table of n, a(n) for n = 1..10000</a>
%H A339389 Rémy Sigrist, <a href="/A339389/a339389.png">Colored scatterplot of the first 25000 terms</a> (where the color denotes the parity of n)
%H A339389 Rémy Sigrist, <a href="/A339389/a339389.txt">C program for A339389</a>
%o A339389 (PARI) { for (n=1, #a = vector(56), print1 (a[n] = sum(i=1, n-1, sum(j=1, n-1, a[i]+a[j]>=a[n-1])) ", ")) }
%o A339389 (C) See Links section.
%Y A339389 Cf. A339388.
%K A339389 nonn,look
%O A339389 1,3
%A A339389 _Rémy Sigrist_, Dec 02 2020