A096565 Final digits of the smallest triangular number starting with n!.

0, 1, 6, 15, 90, 10, 3, 9003, 45300, 9570, 5840220, 533564010, 5384225220, 412190739351, 244816773411, 682660400311, 275258914747246, 710284752537711, 152042178127701610, 6144469158651504786, 8516189439015621936

Offset

1,3

Links

Table of n, a(n) for n=1..21.

Example

a(7) = 3 because the smallest triangular number starting with 7!=5040 is 50403 and so the last digit is 3.

Prog

(PARI) { A096565(n) = my(k, t); k=1; while(1, t=sqrtint(n!*8*10^k)+1; if(t%2==0, t++); t=(t^2-1)/8; if( t\10^k == n!, return(t%10^k)); k++ ); } \\ Max Alekseyev, Apr 25 2009

Crossrefs

Cf. A096564.

Sequence in context: A165570 A260117 A220360 * A013229 A013225 A138547

Adjacent sequences: A096562 A096563 A096564 * A096566 A096567 A096568

Keyword

base,nonn

Author

Jason Earls, Jun 26 2004

Extensions

Extended by Max Alekseyev, Apr 25 2009

Status

approved