Your saying "count all the number" is confusing and doesn't seem to relate to
what follows. Did you mean to say "sum all the number"? -- Darren Duncan
On 2018-07-10 2:02 AM, ToddAndMargo wrote:
Hi All,
Remembering from my school days, a famous mathematician
whose name I forget came up with a formula as a kid
that made math history.
As it transpires, when in school, they disciplined him by
making his count all the number from 1 to some large
number. It took him only a few minutes. They thought
he cheated, so they sent him back with an even larger
number to add up. Same couple of minutes. Blew his
teacher's minds every number they gave him.
Seems he had discovered that if you laid the number
out forward, then reverse underneath
N=5
1 + 2 + 3 + 4 + 5 = 15
5 + 4 + 3 + 2 + 1 = 15
---------------------
6 6 6 6 6 = 30
If you add the columns, you always got N+1 and N times.
And that make the formula
1+2+3..N = (N+1)*N/2
I always have fun recreating this formula from the
forward and reverse tables added as columns.
So feed the following an integer and have fun!
Yup. He blew his teacher's mind!
-T
$ echo "5" | p6 'my $N=slurp(); say $N*($N+1)/2;'
15
$ echo "6" | p6 'my $N=slurp(); say $N*($N+1)/2;'
21
$ echo "100" | p6 'my $N=slurp(); say $N*($N+1)/2;'
5050
