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A068624 a(1) = 9; a(n+1) = smallest triangular number > a(n) formed by adding at least one digit to a(n). 4

%I #6 Dec 05 2013 19:55:11

%S 9,91,1891,18915,1989015,199890015,19998900015,1999989000015,

%T 199999890000015,19999998900000015,1999999989000000015,

%U 199999999890000000015,19999999998900000000015

%N a(1) = 9; a(n+1) = smallest triangular number > a(n) formed by adding at least one digit to a(n).

%F For n>=4, a(n) = 2*10^(2n-4) - 11*10^(n-2) + 15 [From _Max Alekseyev_, Apr 25 2009]

%Y Cf. A068618, A068619, A068621, A068622, A068623.

%K base,more,nonn

%O 1,1

%A _Amarnath Murthy_, Feb 25 2002

%E 3 more terms from _Ray G. Opao_, Dec 09 2004

%E Extended by _Max Alekseyev_, Apr 25 2009

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Last modified March 29 03:51 EDT 2024. Contains 371264 sequences. (Running on oeis4.)