Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #5 Oct 16 2012 14:26:13
%S 1,2,4,9,21,62,159,422,1134,3056,8139,22169,60004,163262,443002
%N First time n appears in the first differences of n*log(n): A217865.
%C Conjecture: the last time n appears is always before the first time n+2 appears.
%C For example the last time 5 appears is at position 135, the first time 7 appears is at position 159.
%o (JavaScript)
%o function firstIndex(arr,k) {
%o p=-1;
%o for (a=1;a<arr.length;a++) if (arr[a]==k) {p=a;return p;}
%o return p;
%o }
%o d=new Array();
%o for (i=1; i<500000; i++)
%o d[i]=Math.floor((i+1)*Math.log(i+1))-Math.floor(i*Math.log(i));
%o for (i=1; i<100; i++) document.write(firstIndex(d, i)+", ");
%Y Cf. A217866.
%K nonn
%O 1,2
%A _Jon Perry_, Oct 16 2012