A108241 Numbers n such that concatenating n and the sum of factorials of the digits of n produces a triangular number.

0, 3, 18, 122, 2111, 12442, 40850, 113347, 202343, 233506, 332600, 435405, 525544, 546233, 554161, 716795, 1000334, 1016217, 1142240, 1244630, 2240515, 2414603, 3103412, 3203757, 3400440, 3413651, 3424213, 3461244, 4430222, 5226150

Offset

1,2

Links

Table of n, a(n) for n=1..30.

Example

18 is in the sequence because 1!+8! = 40321 and 1918*1919/2 = 1840321.

Mathematica

ctnQ[n_]:=Module[{idn=IntegerDigits[n], c}, c=FromDigits[Join[idn, IntegerDigits[ Total[idn!]]]]; IntegerQ[(Sqrt[8c+1]-1)/2]]; Select[ Range[0, 5300000], ctnQ] (* Harvey P. Dale, Sep 20 2012 *)

Crossrefs

Cf. A061602, A109016.

Sequence in context: A355048 A074558 A074564 * A342710 A199421 A305869

Adjacent sequences: A108238 A108239 A108240 * A108242 A108243 A108244

Keyword

base,nonn

Author

Jason Earls, Jun 17 2005

Status

approved