A079872 -id:A079872 - cp's OEIS frontend

A143731 Characteristic function of numbers with at least two distinct prime factors (A024619).

0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1

Offset: 1

Reikku Kulon, Aug 30 2008

a(n) = 1 iff n is divisible by at least two distinct primes; otherwise 0.

Reikku Kulon, Table of n, a(n) for n = 1..10000
Index entries for characteristic functions

Cf. A024619, A079275, A079872, A000961, A001222, A091304, A073093, A001221.

Cf. A215480.

Table[Boole[PrimeNu[n]>1],{n,1,200}] (* Enrique Pérez Herrero, Aug 13 2012 *)

a(n) = abs(A079872(n)) = A057427(A079275(n)).

For n>1: a(n) = 1 - floor(1/A001221(n)). - Enrique Pérez Herrero, Aug 13 2012

A079869 a(1)=1 and for n>1: round(n^(1/Omega(n)))^Omega(n), where Omega(n) is the total number of prime factors of n (A001222).

Original entry on oeis.org

1, 2, 3, 4, 5, 4, 7, 8, 9, 9, 11, 8, 13, 16, 16, 16, 17, 27, 19, 27, 25, 25, 23, 16, 25, 25, 27, 27, 29, 27, 31, 32, 36, 36, 36, 16, 37, 36, 36, 81, 41, 27, 43, 64, 64, 49, 47, 32, 49, 64, 49, 64, 53, 81, 49, 81, 64, 64, 59, 81, 61, 64, 64, 64, 64, 64, 67, 64, 64, 64, 71, 32, 73

Offset: 1

Reinhard Zumkeller, Jan 13 2003

nonn

A079867(n)<=a(n)<=A079869(n); A020639(n)<=a(n)<=A006530(n);

a(m)=m=A079867(m)=A079871(m) iff m is a prime power (A000961).

a(n)=A079868(n)^A001222(n). Cf. A079872, A068794, A068795.

ron[n_]:=Module[{c=PrimeOmega[n]},Round[n^(1/c)]^c]; Join[{1},Array[ ron,80,2]] (* Harvey P. Dale, Jun 17 2020 *)

cp's OEIS Frontend

A143731 Characteristic function of numbers with at least two distinct prime factors (A024619).

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