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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 Antti Karttunen, Table of n, a(n) for n = 1..20000 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 Cf. A000203, A000396, A324213, A325817, A325826, A325961, A325966, A325968. Sequence in context: A290270 A168275 A325968 * A120224 A210471 A183107 Adjacent sequences:  A325815 A325816 A325817 * A325819 A325820 A325821 KEYWORD nonn AUTHOR Antti Karttunen, May 29 2019 STATUS approved

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Last modified August 1 06:45 EDT 2021. Contains 346384 sequences. (Running on oeis4.)