A377991 -id:A377991 - cp's OEIS frontend

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

Antti Karttunen, Nov 15 2024

nonn

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

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

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

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))));

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

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

cp's OEIS Frontend

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.

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