A353788 a(n) = 1 if the number of divisors of n is either 2 or 4, otherwise 0.

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

Offset

1

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for characteristic functions

Index entries for sequences computed from exponents in factorization of n

Formula

a(n) = 1 if A010052(n) == 0 [n is not a square] and A000005(n) <= 4, otherwise 0.

a(n) = [A084115(n) == 1], where [ ] is the Iverson bracket.

a(n) = 1 if A101296(n) is either 2, 4 or 5, otherwise 0.

For n > 1, a(n) = A353799(n) - A302048(n).

Mathematica

a[n_] := If[MemberQ[{2, 4}, DivisorSigma[0, n]], 1, 0]; Array[a, 120] (* Amiram Eldar, May 13 2022 *)

Prog

(PARI) A353788(n) = (!issquare(n) && (numdiv(n)<=4));
(PARI) A353788(n) = (isprime(n) || (4==numdiv(n)));

Crossrefs

Characteristic function of A084116.

Cf. A000005, A000290, A010051, A010052, A101296, A302048, A353799.

Cf. also A353787.

Sequence in context: A181632 A105565 A332814 * A348737 A285418 A344617

Adjacent sequences: A353785 A353786 A353787 * A353789 A353790 A353791

Keyword

nonn

Author

Antti Karttunen, May 13 2022

Status

approved