A215113 a(n) is the number of different prime divisors of A214723(n).

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

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

G. C. Greubel, Table of n, a(n) for n = 1..5000

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

Cf. A001221, A214723.

Sequence in context: A114284 A238303 A023575 * A058978 A105446 A367817

Adjacent sequences: A215110 A215111 A215112 * A215114 A215115 A215116

Keyword

nonn

Author

Vladimir Shevelev, Aug 03 2012

Status

approved