8 lines
423 B
Markdown
8 lines
423 B
Markdown
Pentagonal numbers are generated by the formula, `Pn=n(3n-1)/2`. The first ten pentagonal numbers are:
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> 1, 5, 12, 22, 35, 51, 70, 92, 117, 145, ...
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It can be seen that `P4 + P7 = 22 + 70 = 92 = P8`. However, their difference, `70 - 22 = 48`, is not pentagonal.
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Find the pair of pentagonal numbers, Pj and Pk, for which their sum and difference are pentagonal and `D = | Pk - Pj |` is minimised; what is the value of D?
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