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A367175
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a(n) = Sum_{d|n} (-1)^[d is prime] * d, where [] denotes the Iverson bracket.
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2
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1, -1, -2, 3, -4, 2, -6, 11, 7, 4, -10, 18, -12, 6, 8, 27, -16, 29, -18, 28, 12, 10, -22, 50, 21, 12, 34, 38, -28, 52, -30, 59, 20, 16, 24, 81, -36, 18, 24, 76, -40, 72, -42, 58, 62, 22, -46, 114, 43, 79, 32, 68, -52, 110, 40, 102, 36, 28, -58, 148, -60, 30
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OFFSET
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1,3
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LINKS
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FORMULA
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Conjecture: {k: a(k) divides sigma(k)} = {1, 2, 3, 6, 14, 15, 35}.
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MAPLE
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Isprime := n -> if isprime(n) then 1 else 0 fi:
a := n -> local d; add((-1)^Isprime(d) * d, d in NumberTheory:-Divisors(n)):
seq(a(n), n = 1..62);
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MATHEMATICA
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Array[DivisorSum[#, (-1)^Boole[PrimeQ[#]]*# &] &, 62] (* Michael De Vlieger, Nov 10 2023 *)
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PROG
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(SageMath)
def A367175(n): return sum((-1)^is_prime(d)*d for d in divisors(n))
print([A367175(n) for n in range(1, 63)])
(PARI) a(n) = sumdiv(n, d, (-1)^isprime(d)*d); \\ Michel Marcus, Nov 10 2023
(Python)
from sympy import divisor_sigma, primefactors
def A367175(n): return divisor_sigma(n)-(sum(primefactors(n))<<1) # Chai Wah Wu, Nov 10 2023
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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STATUS
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approved
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