A076971 a(1) = 1, a(n+1)= smallest triangular number greater than the n-th partial sum.

1, 3, 6, 15, 28, 55, 120, 231, 465, 946, 1891, 3828, 7626, 15225, 30628, 61075, 122265, 244650, 489555, 979300, 1959210, 3918600, 7838820, 15677200, 31359240, 62714400, 125429041, 250868800, 501732003, 1003497600, 2006959690

Offset

1,2

Links

Table of n, a(n) for n=1..31.

Maple

a[1] := 1:a[2] := 3:for n from 3 to 145 do a[n] := sum(a[i], i=1..n-1); a[n] := ceil(evalf(-1/2+1/2*sqrt(1+8*a[n])+10^(-19), 100)):a[n] := a[n]*(a[n]+1)/2: od:seq(a[k], k=1..145);

Crossrefs

Cf. A076972.

Sequence in context: A234848 A300761 A069712 * A103529 A185378 A285563

Adjacent sequences: A076968 A076969 A076970 * A076972 A076973 A076974

Keyword

nonn

Author

Amarnath Murthy, Oct 21 2002

Extensions

More terms from Sascha Kurz, Jan 22 2003

Status

approved