id:A121338 - OEIS Search Results

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Pentagonal numbers P(k) that are one-third of other pentagonal numbers: P(k) such that 3*P(k)=P(m) for some m>k.

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70, 511258935, 3732600255368600, 27250975409595074561065, 198953975772318806945317308330 (list; graph; listen)

	OFFSET	`1,1`
	FORMULA	`a(n)=((A001835(6n-2))^2-1)/24`
	EXAMPLE	`a(1)=((A001835(4))^2-1)/24=(41^2-1)/24=70; this number and 3*70=210 are pentagonal numbers (in A000326).`
	CROSSREFS	`Cf. The k values are (A001835(6n-2)+1)/6, the m values are (A001834(6n-3)+1)/6.` `Sequence in context: A103165 A116276 A056666 this_sequence A087043 A126648 A126650` `Adjacent sequences: A121335 A121336 A121337 this_sequence A121339 A121340 A121341`
	KEYWORD	`nonn`
	AUTHOR	`Franz Vrabec (franz.vrabec(AT)planetuniqa.at), Aug 28 2006`

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Last modified August 29 14:50 EDT 2008. Contains 143238 sequences.