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A003972
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Moebius transform of A003961; a(n) = phi(A003961(n)), where A003961 shifts the prime factorization of n one step towards the larger primes.
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38
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1, 2, 4, 6, 6, 8, 10, 18, 20, 12, 12, 24, 16, 20, 24, 54, 18, 40, 22, 36, 40, 24, 28, 72, 42, 32, 100, 60, 30, 48, 36, 162, 48, 36, 60, 120, 40, 44, 64, 108, 42, 80, 46, 72, 120, 56, 52, 216, 110, 84, 72, 96, 58, 200, 72, 180, 88, 60, 60, 144, 66, 72, 200, 486, 96, 96, 70
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OFFSET
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1,2
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LINKS
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FORMULA
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Multiplicative with a(p^e) = (q-1)q^(e-1) where q = nextPrime(p). - David W. Wilson, Sep 01 2001
Sum_{k=1..n} a(k) ~ c * n^2, where c = (3/Pi^2) * Product_{p prime} ((p^2-p)/(p^2 - nextPrime(p)) = 1.2547593344... . - Amiram Eldar, Nov 18 2022
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MATHEMATICA
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b[1] = 1; b[p_?PrimeQ] := b[p] = Prime[ PrimePi[p] + 1]; b[n_] := b[n] = Times @@ (b[First[#]]^Last[#] &) /@ FactorInteger[n]; a[n_] := Sum[ MoebiusMu[n/d]*b[d], {d, Divisors[n]}]; Table[a[n], {n, 1, 70}] (* Jean-François Alcover, Jul 18 2013 *)
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PROG
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(PARI) A003972(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); eulerphi(factorback(f)); }; \\ Antti Karttunen, Aug 20 2020
(Python)
from math import prod
from sympy import nextprime, factorint
def A003972(n): return prod((q:=nextprime(p))**(e-1)*(q-1) for p, e in factorint(n).items()) # Chai Wah Wu, Jul 18 2022
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CROSSREFS
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KEYWORD
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nonn,mult
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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