A068097 a(1) = 1; a(n+1) = smallest triangular numbers starting with a(n).

1, 10, 105, 10585, 105858525, 10585852585252500, 105858525852525008525250025000000, 10585852585252500852525002500000085252500250000002500000000000000

Offset

1,2

Links

Table of n, a(n) for n=1..8.

Formula

a(n+1) = floor((sqrt(8*10^floor(log(a(n))/log(10))*a(n)+1)+1)/2)*(floor((sqrt(8*10^floor(log(a(n))/log(10))*a(n)+1)+1)/2)+1)/2. - Benoit Cloitre, Feb 25 2002

Prog

(PARI) /* with 1000 significant digits : */ a(1)=1, a(2)=10 and for n>2 s=10; for(i=1, 10, s=floor((sqrt(8*10^floor(log(s)/log(10))*s+1)+1)/2)*(floor((sqrt(8*10^floor(log(s)/log(10))*s+1)+1)/2)+1)/2; print1(s, ", "); );

Crossrefs

Sequence in context: A087599 A337826 A226360 * A190956 A142987 A078192

Adjacent sequences: A068094 A068095 A068096 * A068098 A068099 A068100

Keyword

base,nonn

Author

Amarnath Murthy, Feb 19 2002

Extensions

More terms from Vladeta Jovovic, Feb 24 2002

More terms from Benoit Cloitre, Mar 07 2002

Status

approved