A377990 a(n) = sigma(sigma(A350388(n))) * sigma(sigma(A350389(n))), where A350388 and A350389 are the largest unitary divisor of n that is a square, and the largest unitary divisor of n that is an exponentially odd number, respectively.

1, 4, 7, 8, 12, 28, 15, 24, 14, 39, 28, 56, 24, 60, 60, 32, 39, 56, 42, 96, 63, 91, 60, 168, 32, 96, 90, 120, 72, 195, 63, 104, 124, 120, 124, 112, 60, 168, 120, 234, 96, 252, 84, 224, 168, 195, 124, 224, 80, 128, 195, 192, 120, 360, 195, 360, 186, 234, 168, 480, 96, 252, 210, 128, 224, 403, 126, 312, 252, 403, 195

Offset: 1

Author

Antti Karttunen, Nov 15 2024

Keywords

• nonn

Comments

Differs from A051027 at 52, 98, 156, 164, 245, ..., = A377991.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..20000
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A051027, A350388, A350389, A351568, A351569, A377991.

Programs

PARI

A350388(n) = { my(m=1, f=factor(n)); for(k=1,#f~,if(0==(f[k,2]%2), m *= (f[k,1]^f[k,2]))); (m); };
A350389(n) = { my(m=1, f=factor(n)); for(k=1,#f~,if(1==(f[k,2]%2), m *= (f[k,1]^f[k,2]))); (m); };
A377990(n) = (sigma(sigma(A350388(n))) * sigma(sigma(A350389(n))));

Formula

a(n) = A051027(A350388(n)) * A051027(A350389(n)).

a(n) = sigma(A351568(n)) * sigma(A351569(n)).