OFFSET
1,1
COMMENTS
Includes 5*10^(2*k+1)-5*10^k and 5*10^(2*k+1)+5*10^k for all k. - Robert Israel, Aug 14 2018
LINKS
Robert Israel, Table of n, a(n) for n = 1..1890
EXAMPLE
1485 and 10000 - 1485 = 8515 both are triangular numbers.
MAPLE
f:= d -> op(sort(convert(select(t -> (t >= 10^(d-1) and t < 10^d), map(t -> (t^2-1)/8, select(t -> t > 0, map(t -> subs(t, x),
{isolve(x^2+y^2=8*10^d+2)})))), list))):
seq(f(d), d=1..20); # Robert Israel, Aug 14 2018
MATHEMATICA
Select[Accumulate[Range[50000]], IntegerQ[Sqrt[8*(10^(IntegerLength[#]) - #) + 1]] &] (* Jayanta Basu, Aug 05 2013 *)
CROSSREFS
KEYWORD
AUTHOR
Amarnath Murthy, Mar 07 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 17 2002
Seven additional terms from Jayanta Basu, Aug 05 2013
STATUS
approved