id:A045745 - OEIS Search Results

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Numbers n such that sum of proper divisors s(n) is a triangular number T(k).

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1, 2, 3, 4, 5, 6, 7, 11, 13, 14, 16, 17, 18, 19, 23, 24, 25, 28, 29, 31, 33, 36, 37, 41, 43, 47, 51, 53, 54, 59, 61, 66, 67, 71, 73, 79, 83, 89, 91, 97, 101, 103, 107, 109, 112, 113, 123, 127, 131, 135, 137, 139, 149, 151, 157, 163, 167, 172, 173, 179, 181, 191, 193 (list; graph; listen)

	OFFSET	`1,2`
	EXAMPLE	`s(14)=1+2+7=10 is a triangular number. In fact T(4)=10.`
	MATHEMATICA	`tri[ n_ ] := Module[ {}, a=Floor[ N[ Sqrt[ 2n ] ] ]; a(a+1)/2==n ]; Select[ Range[ 300 ], tri[ Apply[ Plus, Divisors[ # ] ]-# ]& ]`
	CROSSREFS	`Cf. A000217.` `Sequence in context: A032976 A115037 A090563 this_sequence A054010 A051948 A103539` `Adjacent sequences: A045742 A045743 A045744 this_sequence A045746 A045747 A045748`
	KEYWORD	`nonn,easy`
	AUTHOR	`Felice Russo (felice.russo(AT)katamail.com)`
	EXTENSIONS	`More terms from Erich Friedman (erich.friedman(AT)stetson.edu).`

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Last modified November 21 14:49 EST 2008. Contains 150807 sequences.

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