A072517 Smallest triangular number beginning with the n-th triangular number other than itself.

10, 36, 66, 105, 153, 210, 2850, 3655, 4560, 5565, 666, 780, 9180, 10585, 12090, 13695, 153181, 1711, 190036, 210276, 231540, 253116, 276396, 3003, 325221, 351541, 378015, 406351, 435711, 4656, 496506, 528906, 561270, 595686, 630003

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

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

Maple

f:= proc(t) local k, s, r;
    for k from 1 do
      s:= ceil(sqrt(1+8*10^k*t));
      if s::even then s:= s+1 fi;
      r:= (s^2-1)/8 - 10^k*t;
      if r < 10^k then
        return 10^k*t + r
      fi
    od
end proc:
map(f, [seq(i*(i+1)/2, i=1..100)]); # Robert Israel, Mar 19 2018

Crossrefs

Cf. A072518.

Sequence in context: A117404 A359959 A309783 * A271912 A288947 A328146

Adjacent sequences: A072514 A072515 A072516 * A072518 A072519 A072520

Keyword

nonn,base,look

Author

Amarnath Murthy, Jul 31 2002

Extensions

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

Status

approved