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 A325970 a(n) is the largest k <= A066503(n) such that k and (2n-sigma(n)) [= A033879(n)] are relatively prime. 7
 0, 0, -1, 2, -1, -1, -1, 6, 6, -1, -1, 5, -1, -1, -1, 14, -1, 11, -1, 9, -1, -1, -1, 17, 20, -1, 23, 1, -1, -1, -1, 30, -1, -1, -1, 30, -1, -1, -1, 29, -1, -1, -1, 21, 29, -1, -1, 41, 42, 40, -1, 25, -1, 47, -1, 41, -1, -1, -1, 29, -1, -1, 41, 62, -1, -1, -1, 33, -1, -1, -1, 65, -1, -1, 59, 37, -1, -1, -1, 69, 78 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS a(n) = n-k for the least k >= A007947(n) such that n-k and n-(sigma(n)-k) are relatively prime. LINKS Antti Karttunen, Table of n, a(n) for n = 1..16384 Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537 FORMULA a(n) = n - A325971(n). For n >= 3, a(A005117(n)) = -1. PROG (PARI) A007947(n) = factorback(factorint(n)[, 1]); \\ From A007947 A325970(n) = { my(s=sigma(n)); forstep(k=n-A007947(n), -oo, -1, if(1==gcd(k, n+n-sigma(n)), return(k))); }; \\ Or alternatively: A325970(n) = { my(s=sigma(n)); for(i=A007947(n), s, if(1==gcd(n-i, n-(s-i)), return(n-i))); }; CROSSREFS Cf. A000203, A005117, A007947, A033879, A066503, A324213, A325826, A325960, A325967, A325971, A325972. Sequence in context: A064992 A187783 A089759 * A088152 A049270 A025269 Adjacent sequences:  A325967 A325968 A325969 * A325971 A325972 A325973 KEYWORD sign AUTHOR Antti Karttunen, May 31 2019 STATUS approved

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Last modified July 29 09:31 EDT 2021. Contains 346344 sequences. (Running on oeis4.)