login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 59th year, we have over 358,000 sequences, and we’ve crossed 10,300 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A047824 Becomes prime after exactly 5 iterations of f(x) = sum of prime factors of x. 0

%I

%S 134,177,262,268,398,422,466,524,531,536,573,614,669,706,742,753,796,

%T 817,818,844,849,898,915,921,932,933,934,974,1006,1048,1072,1149,1165,

%U 1202,1222,1227,1228,1238,1239,1243,1294,1322,1347,1354,1385,1393,1398

%N Becomes prime after exactly 5 iterations of f(x) = sum of prime factors of x.

%C f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.

%t p5iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&,n,5]] == {False,False,False,False,False,True}; Select[Range[2000],p5iQ] (* _Harvey P. Dale_, May 21 2015 *)

%K nonn

%O 1,1

%A _David W. Wilson_

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 27 14:41 EST 2022. Contains 358405 sequences. (Running on oeis4.)