A389209 a(n) = gcd(A389207(n), A389208(n)).

4, 52, 8, 4, 4, 24, 4, 8, 4, 4, 4, 4, 4, 4, 8, 8, 8, 16, 8, 8, 4, 24, 4, 8, 4, 4, 8, 8, 4, 16, 4, 4, 8, 24, 4, 12, 4, 8, 4, 4, 4, 12, 8, 40, 4, 8, 8, 4, 4, 8, 4, 4, 12, 4, 8, 8, 4, 4, 4, 24, 8, 4, 4, 4, 208, 4, 4, 8, 4, 8, 40, 4, 4, 4, 4, 4, 8, 8, 4, 8, 8, 48, 4, 4, 8, 24, 8, 8, 4, 8, 4, 8, 8, 60, 24, 4, 8, 4, 16

Offset

1,1

Links

Antti Karttunen, Table of n, a(n) for n = 1..20410

Formula

a(n) = A326129(A228058(n)) = gcd(A389207(n), A389208(n)).

Prog

(PARI)
up_to = 20410;
isA228058(n) = if(!(n%2)||(omega(n)<2), 0, my(f=factor(n), y=0); for(i=1, #f~, if(1==(f[i, 2]%4), if((1==y)||(1!=(f[i, 1]%4)), return(0), y=1), if(f[i, 2]%2, return(0)))); (y));
A228058list(up_to) = { my(v=vector(up_to), k=0, n=0); while(k<up_to, n++; if(isA228058(n), k++; v[k] = n)); (v); };
v228058 = A228058list(up_to);
A228058(n) = v228058[n];
A326129(n) = { my(s=sigma(n), c=core(n)); gcd((s-c-n), (n-c)); };
A389209(n) = A326129(A228058(n));

Crossrefs

Cf. A228058, A326129, A389207, A389208.

Cf. also A325375.

Sequence in context: A000516 A182044 A000854 * A377382 A232517 A329009

Adjacent sequences: A389206 A389207 A389208 * A389210 A389211 A389212

Keyword

nonn

Author

Antti Karttunen, Sep 29 2025

Status

approved