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A072591
In prime factorization of n replace multiplication with bitwise logical 'and'.
4
1, 2, 3, 2, 5, 2, 7, 2, 3, 0, 11, 2, 13, 2, 1, 2, 17, 2, 19, 0, 3, 2, 23, 2, 5, 0, 3, 2, 29, 0, 31, 2, 3, 0, 5, 2, 37, 2, 1, 0, 41, 2, 43, 2, 1, 2, 47, 2, 7, 0, 1, 0, 53, 2, 1, 2, 3, 0, 59, 0, 61, 2, 3, 2, 5, 2, 67, 0, 3, 0, 71, 2, 73, 0, 1, 2, 3, 0, 79, 0, 3, 0, 83, 2, 1, 2, 1, 2, 89, 0, 5, 2, 3, 2
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.
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