1+2 - nx(n+1)/2=2x(2+1)/2=2x3/2=6/2=3, 1+2+3 - nx(n+1)/2=3x(3+1)/2=3x4/2=12/2=6, 1+2+3+4 - nx(n+1)/2=4x(4+1)/2=4x5/2=20/2=10, 1+2+3+4+5 - nx(n+1)/2=5x(5+1)/2=5x6/2=30/2=15, 1+2+3+4+5+6 - nx(n+1)/2=6x(6+1)/2=6x7/2=42/2=21, 1+2+3+4+5+6+7 - nx(n+1)/2=7x(7+1)/2=7x8/2=56/2=28, 1+2+3+4+5+6+7+8 - nx(n+1)/2=8x(8+1)/2=8x9/2=72/2=36, 1+2+3+4+5+6+7+8+9 - nx(n+1)/2=9x(9+1)/2=9x10/2=90/2=45, 1+2+3+............+97+98+99 - nx(n+1)/2=99x(99+1)/2=99x100/2=4950,

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