Stage: 5 Challenge Level: 
Sum the series $$1 \times 1! + 2 \times 2! + 3 \times 3! +...+n \times n!$$
Powers & roots. Stage 5 - Reviewed 2012. Short problems. Factorials. Mathematical reasoning & proof. Inequality/inequalities. Manipulating algebraic expressions/formulae. alphas. epsilons. Summation of series.
Published September 2002.
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