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A325818 a(n) is the largest k <= sigma(n) such that n-k and n-(sigma(n)-k) are relatively prime. 11
1, 3, 4, 7, 6, 7, 8, 15, 13, 17, 12, 27, 14, 23, 22, 31, 18, 38, 20, 41, 32, 35, 24, 59, 31, 39, 40, 29, 30, 71, 32, 63, 46, 53, 48, 91, 38, 59, 56, 89, 42, 95, 44, 83, 76, 69, 48, 123, 57, 93, 70, 95, 54, 119, 72, 119, 80, 89, 60, 167, 62, 95, 104, 127, 84, 143, 68, 125, 94, 143, 72, 194, 74, 113, 124, 137, 96 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
a(n) is the largest k <= sigma(n) such that (-n + k) and (n-sigma(n))+k are coprime.
LINKS
FORMULA
a(n) = A000203(n) - A325817(n).
a(n) = n + A325826(n).
For all n:
a(A000396(n)) = A000396(n)+1.
a(n) >= A325961(n).
a(n) >= A325966(n).
a(n) >= A325968(n).
PROG
(PARI) A325818(n) = { my(s=sigma(n)); for(i=0, s, if(1==gcd(n-i, n-(s-i)), return(s-i))); };
CROSSREFS
Sequence in context: A290270 A168275 A325968 * A120224 A210471 A183107
KEYWORD
nonn
AUTHOR
Antti Karttunen, May 29 2019
STATUS
approved

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Last modified March 29 07:27 EDT 2024. Contains 371265 sequences. (Running on oeis4.)