OFFSET
1,1
LINKS
Paolo P. Lava, Table of n, a(n) for n = 1..100
EXAMPLE
2223 is a member, since the 2223rd triangular number is 2471976 and 247 + 1976 = 2223.
MATHEMATICA
lst = {}; Do[t = n(n + 1)/2; p=10; While[t>p, If[Mod[t, p]+Floor[t/p]==n, AppendTo[lst, n]]; p*=10], {n, 200000}]; lst
Select[Range[10^5], Function[n, Total@ Boole@ Function[k, n == First@ # + Last@ # & /@ Map[FromDigits /@ TakeDrop[IntegerDigits@ k, #] &, Range[IntegerLength@ k - 1]]][n (n + 1)/2] > 0]] (* Michael De Vlieger, May 07 2016, Version 10.2 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Giovanni Resta, Jan 21 2006
STATUS
approved