A138586 - OEIS

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A138586

a(1) = 1; a(n) = a(n-1) + (n!)^7.

1, 129, 280065, 4586751489, 358322666751489, 100306488365546751489, 82606511560391889386751489, 173238283180457843219993066751489, 828593116199250458889895450218986751489 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,2`
	COMMENTS	`After a(1) = 1 these are all divisible by 3. a(n)/3 is prime (i.e. a(n) is semiprime) for n = 2, 4 (i.e. (1!)^7 + (2!)^7 + (3!)^7 + (4!)^7 = 4586751489 = 3 * 1528917163) and then when next?`
	FORMULA	`a(n) = SUM{k=1..n] (k!)^7 = SUM[k=1..n] A001015(A000142(n)).`
	CROSSREFS	`Cf. A000142, A001015, A104344, A100288.` `Sequence in context: A143006 A176368 A183553 * A103347 A113489 A043604` `Adjacent sequences: A138583 A138584 A138585 * A138587 A138588 A138589`
	KEYWORD	`easy,nonn`
	AUTHOR	`Jonathan Vos Post (jvospost3(AT)gmail.com), May 18 2008`

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Last modified February 13 08:12 EST 2012. Contains 205451 sequences.