7thoctagonalnumber

<-- Enter octagonal number statement
  

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Calculate octagonal number 7

The formula for octagonal number n is as follows
O_n = n(3n - 2)

Given n = 7, we have:
O_n = 7(3(7) - 2)
O_n = 7(21 - 2)
O_n = 7(19)
O₇ = 133

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