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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

Index entries for sequences related to sigma(n)

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.)