A238091 A bisection of A136259.
1, 4, 9, 18, 31, 33, 39, 56, 58, 94, 96, 103, 156, 239, 245, 253, 255, 257, 275, 277, 420, 610, 788, 790, 792, 1070, 1665, 1667, 1669
Offset: 1
Formula
a(n) = A136259(2*n-1). - Jinyuan Wang, Mar 04 2020
This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
The sieve starts as follows. Initially no numbers are crossed out. Take a(1)=1 and cross it out. The next uncrossed number is 2, so a(2)=2. Now cross out 2 and 2+1. The next uncrossed number is 4, so a(3)=4. Then cross out 4, 4+3, 4+3+2, 4+3+2+1. The next uncrossed number is 5, and so on.
int limit = 15707; //highest number in the sieve (inclusive)
boolean[] n = new boolean[limit + 1];
int index = 1;
for ( int i = 1; i < n.length; i++ ) {
if ( !n[i] ) {
System.out.println(index++ + " " + i);
int j = i, k = i;
while ( k + j - 1 < n.length && j > 0 ) {
k += --j;
n[k] = true;
}
}
}
// Griffin N. Macris, Mar 24 2016
nn = 200; a = Range@ nn; Do[If[Length@a >= n, a = Complement[a, Function[k, Rest@ Map[Total, MapIndexed[Take[k, #] &, Range@ Max@ k]]]@ Reverse@ Range@ a[[n]]]], {n, 2, nn}]; a (* Michael De Vlieger, Mar 25 2016 *)
mx:= 10000: # maximal index needed
b:= proc(n) n end:
a:= proc(n) option remember; global mx; local h, t;
if n=0 then 0 else a(n-1); t:= b(n);
if n+t<=mx then h:=b(t+n); b(t+n):=h+n fi; t
fi
end:
seq(a(n), n=1..100); # Alois P. Heinz, Mar 04 2015
mx = 10000 (* maximal index needed *); b[n_] := n; a[n_] := a[n] = Module[{h, t}, If[n == 0, 0, a[n-1]; t = b[n]; If[n+t <= mx, h = b[t+n]; b[t+n] = h+n]; t]]; Table[a[n], {n, 1, 100}] (* Jean-François Alcover, Oct 24 2016, after Alois P. Heinz *)
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