id:A047820 - OEIS Search Results

Search: id:A047820

Displaying 1-1 of 1 results found.

page 1

Becomes prime after exactly 1 iteration of f(x) = sum of prime factors of x.

+0
4

4, 6, 8, 9, 10, 12, 16, 18, 20, 22, 24, 25, 27, 32, 34, 36, 40, 44, 48, 49, 50, 54, 58, 64, 68, 72, 80, 81, 82, 88, 96, 100, 108, 116, 118, 121, 125, 128, 136, 142, 144, 160, 162, 164, 165, 169, 176, 192, 200, 202, 210, 214, 216, 232, 236, 242, 243, 250, 256, 272 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.`
	MATHEMATICA	`Select[ Range@280, (fi = FactorInteger@#; Plus @@ Last /@ fi > 1 && PrimeQ[Plus @@ First /@ fi]) &] (from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 09 2005)`
	CROSSREFS	`Sequence in context: A066071 A067013 A071070 this_sequence A034878 A116661 A109104` `Adjacent sequences: A047817 A047818 A047819 this_sequence A047821 A047822 A047823`
	KEYWORD	`nonn`
	AUTHOR	`David W. Wilson (davidwwilson(AT)comcast.net)`

page 1

Search completed in 0.002 seconds

Last modified July 19 08:04 EDT 2008. Contains 142098 sequences.

AT&T Labs Research