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A353381
Number of divisors of n not in A353355.
3
0, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 2, 1, 2, 2, 2, 1, 2, 1, 3, 3, 3, 1, 3, 1, 2, 1, 2, 1, 5, 1, 2, 2, 3, 2, 2, 1, 2, 3, 4, 1, 5, 1, 3, 2, 3, 1, 4, 1, 3, 2, 2, 1, 3, 3, 3, 3, 2, 1, 5, 1, 3, 3, 2, 2, 5, 1, 3, 2, 5, 1, 3, 1, 2, 2, 2, 2, 5, 1, 6, 2, 3, 1, 5, 3, 2, 3, 4, 1, 5, 3, 3, 2, 3, 2, 4, 1, 2, 2, 3, 1, 5, 1, 3, 5
OFFSET
1,6
FORMULA
a(n) = Sum_{d|n} 1-A353380(d).
a(n) = A000005(n) - A353382(n).
a(p) = 1 for all primes p.
a(n) = a(A003961(n)) = a(A348717(n)), for all n >= 1.
PROG
(PARI)
A332823(n) = { my(f = factor(n), u=(sum(k=1, #f~, f[k, 2]*2^primepi(f[k, 1]))/2)%3); if(2==u, -1, u); };
A353354(n) = sumdiv(n, d, A332823(d));
A353380(n) = (0==A353354(n));
A353381(n) = sumdiv(n, d, !A353380(d));
KEYWORD
nonn
AUTHOR
Antti Karttunen, Apr 19 2022
STATUS
approved