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#20 by Joerg Arndt at Tue Aug 13 01:55:58 EDT 2024
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#19 by Michel Marcus at Mon Aug 12 23:41:02 EDT 2024
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#18 by Chai Wah Wu at Mon Aug 12 22:26:39 EDT 2024
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#17 by Chai Wah Wu at Mon Aug 12 22:26:32 EDT 2024
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| PROG
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return -(1<<len(g:=factorint(m).values()))+prod(e+1 for e in g) # Chai Wah Wu, Aug 12 2024
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#16 by Chai Wah Wu at Mon Aug 12 22:26:23 EDT 2024
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| PROG
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(Python)
from math import prod, isqrt
from sympy import mobius, factorint
def A174961(n):
def f(x): return n+sum(mobius(k)*(x//k**2) for k in range(1, isqrt(x)+1))
m, k = n, f(n)
while m != k:
m, k = k, f(k)
return -(1<<len(g:=factorint(m).values()))+prod(e+1 for e in g) # Chai Wah Wu, Aug 12 2024
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| STATUS
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approved
editing
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#15 by OEIS Server at Sat Dec 09 07:07:11 EST 2023
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| LINKS
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Amiram Eldar, <a href="/A174961/b174961_1.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from G. C. Greubel)
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#14 by Peter Luschny at Sat Dec 09 07:07:11 EST 2023
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Discussion
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| Sat Dec 09
| 07:07
| OEIS Server: Installed new b-file as b174961.txt. Old b-file is now b174961_1.txt.
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#13 by Joerg Arndt at Sat Dec 09 04:23:26 EST 2023
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#12 by Amiram Eldar at Sat Dec 09 03:41:41 EST 2023
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#11 by Amiram Eldar at Sat Dec 09 03:38:11 EST 2023
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| EXAMPLE
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For n = 4, the fourth nonsquarefree number is A013929(4) = 12 which has 2 non-unitary divisors, 42 and 126. Therefore a(4) = 2.
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