A355828 - OEIS

%I #12 Jul 20 2022 18:36:10

%S 1,-3,-1,8,-1,3,-1,-24,0,3,-1,-8,-1,3,1,72,-1,0,-1,-28,1,3,-1,12,0,3,

%T -4,-8,-1,-3,-1,-222,1,3,1,0,-1,3,1,138,-1,-3,-1,-10,0,3,-1,0,0,0,1,

%U -8,-1,12,1,24,-3,3,-1,28,-1,3,0,684,-5,-3,-1,-16,1,-3,-1,12,-1,3,0,-8,1,-3,-1,-538,8,3,-1,8,1,3,-3,30

%N Dirichlet inverse of A342671, the greatest common divisor of sigma(n) and A003961(n), where A003961 is fully multiplicative with a(p) = nextprime(p).

%H Antti Karttunen, <a href="/A355828/b355828.txt">Table of n, a(n) for n = 1..16384</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%F a(1) = 1, and for n > 1, a(n) = -Sum_{d|n, d<n} A342671(n/d) * a(d).

%t f[p_, e_] := NextPrime[p]^e; s[n_] := GCD[DivisorSigma[1, n], Times @@ f @@@ FactorInteger[n]]; a[1] = 1; a[n_] := - DivisorSum[n, a[#] * s[n/#] &, # < n &]; Array[a, 100] (* _Amiram Eldar_, Jul 20 2022 *)

%o (PARI)

%o A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };

%o A342671(n) = gcd(sigma(n), A003961(n));

%o memoA355828 = Map();

%o A355828(n) = if(1==n,1,my(v); if(mapisdefined(memoA355828,n,&v), v, v = -sumdiv(n,d,if(d<n,A342671(n/d)*A355828(d),0)); mapput(memoA355828,n,v); (v)));

%Y Cf. A000203, A003961, A342671.

%Y Cf. also A355829.

%K sign

%O 1,2

%A _Antti Karttunen_, Jul 20 2022