Centered pentagonal number

Centered pentagonal number

A centered pentagonal number is a centered figurate number that represents a pentagon with a dot in the center and all other dots surrounding the center in successive pentagonal layers. The centered pentagonal number for "n" is given by the formula

(5(n-1)^2 + 5(n-1) + 2)} over 2}.

The first few centered pentagonal numbers are

1, 6, 16, 31, 51, 76, 106, 141, 181, 226, 276, 331, 391, 456, 526, 601, 681, 766, 856, 951, 1051, 1156, 1266, 1381, 1501, 1626, 1756, 1891, 2031, 2176, 2326, 2481, 2641, 2806, 2976.

The sequence is Sloane's [http://www.research.att.com/~njas/sequences/A005891 A005891] .

The parity of centered pentagonal numbers follows the pattern even-even-odd-odd, and in base 10 the ones' digits follow the pattern 6-6-1-1.

ee also

*Pentagonal number
*Polygonal number
*Centered polygonal number

External links

*mathworld|title=Centered pentagonal number|urlname=CenteredPentagonalNumber


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