A013322 Golomb-type sequence over triangular numbers.

1, 3, 3, 3, 6, 6, 6, 10, 10, 10, 15, 15, 15, 15, 15, 15, 21, 21, 21, 21, 21, 21, 28, 28, 28, 28, 28, 28, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 45, 45, 45, 45, 45, 45, 45, 45, 45, 45, 55, 55, 55, 55, 55, 55, 55, 55, 55, 55, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66, 66

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

All terms are triangular numbers; a(n) is length of n-th run.

It is understood that a(n) is taken to be the smallest number >= a(n-1) which is compatible with the description.

The apparent idempotence, a(a(n))=a(n), holds while n<191 and breaks after that. - Ivan Neretin, Apr 03 2015

Links

• Ivan Neretin, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A001462.

Programs

Maple

A:= 1,3,3,3:
for n from 4 to 30 do
  t:= n*(n-1)/2;
  A:= A, t$A[n-1]
od:
A; # Robert Israel, Apr 03 2015

Mathematica

a = {1, 3, 3, 3}; Do[a = Join[a, Array[i(i+1)/2&, a[[i]]]], {i, 3, 11}]; a (* Ivan Neretin, Apr 03 2015 *)