OFFSET
1,2
COMMENTS
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..15436
Shyam Sunder Gupta Fascinating Triangular Numbers
EXAMPLE
a(5)=21: 21 is a triangular number and also a Harshad number as 21 is divisible by 2+1=3. So 21 is Harshad triangular number.
MATHEMATICA
TriangularNumberQ[k_] := If[IntegerQ[1/2 (Sqrt[1 + 8 k] - 1)], True, False]; Harshad[k_] := Select[Range[k], IntegerQ[ #/(Plus @@ IntegerDigits[ # ])] &]; TriangularHarshad[k_] := Select[Harshad[k], TriangularNumberQ[#] &]; TriangularHarshad[5886] (* Ant King, Dec 13 2010 *)
A076713 = {}; Do[k = n*(n + 1)*1/2; If[IntegerQ[k/(Plus @@ IntegerDigits[k])], AppendTo[A076713, k]], {n, 1000}]; A076713 (* K. D. Bajpai, Aug 13 2014 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Shyam Sunder Gupta, Oct 26 2002
STATUS
approved