|
%I #17 Nov 28 2021 10:29:52
%S 0,0,1,1,1,2,1,1,1,2,1,3,1,2,3,2,1,2,1,4,3,2,1,3,2,2,2,4,1,6,1,3,3,2,
%T 3,3,1,2,3,4,1,6,1,4,4,2,1,5,2,4,3,4,1,4,3,4,3,2,1,8,1,2,4,4,3,6,1,4,
%U 3,6,1,3,1,2,5,4,3,6,1,5,3,2,1,8,3,2,3,4,1,8,3,4
%N Number of nonrefactorable divisors of n.
%H Antti Karttunen, <a href="/A349658/b349658.txt">Table of n, a(n) for n = 1..20000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/RefactorableNumber.html">Refactorable Number</a>
%F a(n) = A000005(n) - A336041(n).
%F a(n) = A349322(n) - A335182(n). - _Antti Karttunen_, Nov 24 2021
%F a(p) = 1 for odd primes p. - _Wesley Ivan Hurt_, Nov 28 2021
%t a[n_] := DivisorSum[n, 1 &, !Divisible[#, DivisorSigma[0, #]] &]; Array[a, 100] (* _Amiram Eldar_, Nov 24 2021 *)
%o (PARI) a(n) = sumdiv(n, d, d%numdiv(d) != 0); \\ _Michel Marcus_, Nov 24 2021
%Y Cf. A000005, A033950, A336041, A335182, A349322.
%K nonn
%O 1,6
%A _Wesley Ivan Hurt_, Nov 23 2021
|
