OFFSET
1,2
LINKS
MATHEMATICA
(Sqrt[8#+1]-1)/2&/@Select[Flatten[Table[FromDigits/@Tuples[{1, 5, 6}, n], {n, 11}]], OddQ[Sqrt[8#+1 ]]&] (* Harvey P. Dale, Nov 02 2014 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, May 10 2006
STATUS
approved