OFFSET
1,2
COMMENTS
a(n) = a(A007947(n)); n is prime iff a(n)=n;
a(n)=0 iff n is even and one prime factor is of form 4*k+1.
LINKS
Paul Tek, Table of n, a(n) for n = 1..10000
EXAMPLE
a(35) = a(5*7) = a(5) 'and' a(7) = '101' and '111' = '101' = 5.
MATHEMATICA
a[n_] := BitAnd @@ FactorInteger[n][[All, 1]];
Array[a, 100] (* Jean-François Alcover, Nov 16 2021 *)
PROG
(Haskell)
import Data.Bits ((.&.))
a072591 = foldl1 (.&.) . a027746_row -- Reinhard Zumkeller, Jul 05 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jun 23 2002
STATUS
approved