A077694 a(n) = triangular number pertaining to the number f(n) obtained by concatenating first n natural numbers.

1, 78, 7626, 761995, 76205685, 7620753696, 762078456028, 76207888812681, 7620789436823655, 76207893880582233505, 762078938758291471246566, 7620789387578285082874368828, 76207893875782400211463469221291

Offset

1,2

Links

Table of n, a(n) for n=1..13.

Example

a(4) =761995= 1234*1235/2

Mathematica

tno[lst_]:=Module[{n=FromDigits[lst]}, (n(n+1))/2]; tno/@Table[Flatten[ IntegerDigits/@Range[n]], {n, 20}] (* Harvey P. Dale, Aug 16 2011 *)

Crossrefs

Cf. A077692, A077693.

Sequence in context: A328354 A268023 A268016 * A119216 A119236 A126998

Adjacent sequences: A077691 A077692 A077693 * A077695 A077696 A077697

Keyword

base,nonn

Author

Amarnath Murthy, Nov 18 2002

Extensions

More terms from Sascha Kurz, Jan 07 2003

Status

approved