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a(n) = 1 if the number of divisors of n is not larger than 4, otherwise 0.
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%I #11 May 13 2022 18:25:02

%S 1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,0,1,0,1,0,1,1,1,0,1,1,1,0,1,0,1,0,1,1,

%T 1,0,1,1,1,0,1,0,1,0,0,1,1,0,1,0,1,0,1,0,1,0,1,1,1,0,1,1,0,0,1,0,1,0,

%U 1,0,1,0,1,1,0,0,1,0,1,0,0,1,1,0,1,1,1,0,1,0,1,0,1,1,1,0,1,0,0,0,1,0,1,0,0,1,1,0,1,0,1,0,1,0,1,0,0,1,1,0,1,1,1,0,1

%N a(n) = 1 if the number of divisors of n is not larger than 4, otherwise 0.

%H Antti Karttunen, <a href="/A353799/b353799.txt">Table of n, a(n) for n = 1..65537</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%H <a href="/index/Eu#epf">Index entries for sequences computed from exponents in factorization of n</a>

%F a(n) = [A000005(n) <= 4], where [ ] is the Iverson bracket.

%F a(n) = [A101296(n) <= 5].

%F For n > 1, a(n) = A302048(n) + A353788(n).

%t a[n_] := If[DivisorSigma[0, n] <= 4, 1, 0]; Array[a, 120] (* _Amiram Eldar_, May 13 2022 *)

%o (PARI) A353799(n) = (4>=numdiv(n));

%Y Characteristic function of A007964.

%Y Cf. A000005, A101296, A302048, A353788.

%K nonn

%O 1

%A _Antti Karttunen_, May 13 2022