7thpentagonalnumber

<-- Enter pentagonal number statement
  

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Calculate pentagonal number 7

The formula for pentagonal number n is as follows

Pn  =	n(3n - 1)
	2

Given n = 7, we have:

P7  =	7(3(7) - 1)
	2

P7  =	7(21 - 1)
	2

P7  =	7(20)
	2

P7  =	140
	2

P₇ = 70

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