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

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A215113 a(n) is the number of different prime divisors of A214723(n). 2
1, 1, 2, 1, 2, 2, 1, 2, 2, 2, 1, 3, 2, 3, 1, 2, 2, 2, 2, 3, 1, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 3, 2, 3, 3, 2, 2, 2, 2, 2, 3, 1, 3, 3, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
The records of a(n) are a(1)=1, a(3)=2, a(12)=3, a(132)=4,... Is the sequence unbounded?
LINKS
FORMULA
a(n) = A001221(A214723(n)). - Michel Marcus, Feb 08 2016
MATHEMATICA
nn = 2000; ps = Prime[Range[PrimePi[Sqrt[nn]]]]; t = Flatten[Table[ ps[[i]]^2 + ps[[j]]^2, {i, Length[ps]}, {j, i, Length[ps]}]]; t =
Select[t, # <= nn &]; PrimeNu[Sort[Transpose[Select[Tally[t], #[[2]] == 1 &]][[1]]]] (* G. C. Greubel, May 16 2017 *)
CROSSREFS
Sequence in context: A114284 A238303 A023575 * A058978 A105446 A367817
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Aug 03 2012
STATUS
approved

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 April 14 14:16 EDT 2024. Contains 371665 sequences. (Running on oeis4.)