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A058665
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a(n) = gcd(n+1, n-phi(n)).
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1
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2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 5, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 5, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 5, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 7, 1
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OFFSET
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1,1
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COMMENTS
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a(n) = 1 for most n. True for all primes and other integers.
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LINKS
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FORMULA
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a(n) = gcd(n+1, cototient(n)) = gcd(n+1, A051953(n)).
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EXAMPLE
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n = 247 = 13*19, n+1 = 248 = 8*31, phi(247) = 12*18 = 216, cototient(247) = 247-216 = 31, so a(247) = gcd(248,31) = 31.
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MATHEMATICA
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Table[GCD[n+1, n-EulerPhi[n]], {n, 0, 110}] (* Harvey P. Dale, Dec 24 2012 *)
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PROG
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(Python)
from sympy import gcd, totient
def a(n): return gcd(n + 1, n - totient(n))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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