A072517 - OEIS

%I #7 Mar 19 2018 22:10:34

%S 10,36,66,105,153,210,2850,3655,4560,5565,666,780,9180,10585,12090,

%T 13695,153181,1711,190036,210276,231540,253116,276396,3003,325221,

%U 351541,378015,406351,435711,4656,496506,528906,561270,595686,630003

%N Smallest triangular number beginning with the n-th triangular number other than itself.

%H Robert Israel, <a href="/A072517/b072517.txt">Table of n, a(n) for n = 1..10000</a>

%e a(7) = 2850 > 28 is the smallest triangular number beginning with 28 which is the seventh triangular number.

%p f:= proc(t) local k,s,r;

%p     for k from 1 do

%p       s:= ceil(sqrt(1+8*10^k*t));

%p       if s::even then s:= s+1 fi;

%p       r:= (s^2-1)/8 - 10^k*t;

%p       if r < 10^k then

%p         return 10^k*t + r

%p       fi

%p     od

%p end proc:

%p map(f, [seq(i*(i+1)/2, i=1..100)]); # _Robert Israel_, Mar 19 2018

%Y Cf. A072518.

%K nonn,base,look

%O 1,1

%A _Amarnath Murthy_, Jul 31 2002

%E Corrected and extended by Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 25 2003