A355829 - OEIS

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A355829

Dirichlet inverse of A009194, the greatest common divisor of sigma(n) and n, where sigma is the sum of divisors function.

1, -1, -1, 0, -1, -4, -1, 0, 0, 0, -1, 7, -1, 0, -1, 0, -1, 8, -1, 1, 1, 0, -1, -10, 0, 0, 0, -25, -1, 10, -1, 0, -1, 0, 1, 15, -1, 0, 1, -8, -1, 6, -1, -1, 2, 0, -1, 16, 0, 2, -1, 1, -1, -6, 1, 46, 1, 0, -1, -9, -1, 0, 0, 0, 1, 10, -1, 1, -1, 2, -1, -29, -1, 0, 4, -1, 1, 6, -1, 16, 0, 0, -1, 29, 1, 0, -1, 2, -1, -8

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,6

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

Index entries for sequences related to sigma(n)

FORMULA

a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A009194(n/d) * a(d).

MATHEMATICA

s[n_] := GCD[n, DivisorSigma[1, n]]; a[1] = 1; a[n_] := - DivisorSum[n, a[#] * s[n/#] &, # < n &]; Array[a, 100] (* Amiram Eldar, Jul 20 2022 *)

PROG

(PARI)

A009194(n) = gcd(n, sigma(n));

memoA355829 = Map();

A355829(n) = if(1==n, 1, my(v); if(mapisdefined(memoA355829, n, &v), v, v = -sumdiv(n, d, if(d<n, A009194(n/d)*A355829(d), 0)); mapput(memoA355829, n, v); (v)));

CROSSREFS

Cf. A000203, A009194.

Cf. also A355828.

Sequence in context: A127560 A098172 A049759 * A265421 A137252 A228623

Adjacent sequences: A355826 A355827 A355828 * A355830 A355831 A355832

KEYWORD

sign

AUTHOR

Antti Karttunen, Jul 20 2022

STATUS

approved