OFFSET
1,2
COMMENTS
Conjectured to be a permutation of the natural numbers (cf. A099130). The first few fixed points are: 1, 2, 19, 92, 220, 467, 556, 616, 690, 842.
LINKS
EXAMPLE
n=5: ss={1,2,4,6}; triangular numbers > 6 are 10,15,21; but 10-6=4 is in ss, hence a(5)=15-6=9;
n=6, ss={1,2,4,6,9}; triangular numbers > 9 are 10,15,21; but 10-9=4 and 15-9=6 are in ss, hence a(6)=21-9=12 etc.
MATHEMATICA
tr=Table[n(n+1)/2, {n, 100}]; s={1}; a=1; Do[Do[tk=tr[[k]]; If[tk > a, b=tk-a; If[FreeQ[s, b], AppendTo[s, b]; a=b; Break[]]], {k, 100}], {99}]; s (* Zak Seidov, Jul 12 2010 *)
PROG
(PARI) v=[1]; n=1; while(n<100, if(ispolygonal(n+v[#v], 3)&&!vecsearch(vecsort(v), n), v=concat(v, n); n=0); n++); v \\ Derek Orr, Jun 08 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amarnath Murthy, Nov 03 2002
EXTENSIONS
More terms from Reinhard Zumkeller, Sep 28 2004
Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, Jun 08 2007
Further edited by N. J. A. Sloane, Jul 11 2010, Jul 19 2010
STATUS
approved