A099507 a(n) is such that A099506(a(n)) = n.

1, 4, 2, 6, 17, 3, 10, 5, 12, 7, 14, 53, 9, 8, 11, 22, 13, 24, 15, 26, 99, 103, 28, 107, 30, 19, 32, 111, 16, 23, 18, 25, 42, 20, 29, 46, 31, 48, 33, 50, 209, 35, 211, 56, 37, 58, 217, 39, 60, 21, 41, 64, 43, 66, 245, 45, 72, 47, 74, 49, 27, 51, 34, 267, 80, 36, 82, 277, 38, 57

Offset: 1

Author

Mark Hudson (mrmarkhudson(AT)hotmail.com), Oct 20 2004

Keywords

• easy
• nonn

Comments

a(199) > 10^6 if it exists. - Robert Israel, Jun 17 2015

Examples

			Gives the positions in the sequence A099506 at which the integers n>0 appear. That sequence begins: 1,3,6,2,8,4,... so a(1)=1, a(2)=4, a(3)=2, etc.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..198
• Robert Israel, Table of n, a(n) for n = 1..10000 with 0 for entries greater than 10^6 (if they exist at all)

Crossrefs

Cf. A099506.

Programs

MATLAB

N = 10^6;
M = 10*N;  % search up to A099506(N) while A099507 < M
% returns 0 for entries not found
B = zeros(1, M);
A = zeros(1, N);
A(1) = 1;
B(1) = 1;
for n = 2:N
  t = mod(-A(n-1)-1,n)+1;
  bm = t + [0:floor((M-t)/n)]*n;
  bz = find(B(bm)==0,1);
  if numel(bz)==0
      break
  end
  m = t + n*(bz-1);
  A(n) = m;
  B(m) = n;
end;
B(1:1000) % Robert Israel, Jun 17 2015