A377990 -id:A377990 - cp's OEIS frontend

A377991 Numbers k such that A351568(k) and A351569(k) are not coprime, where A351568 and A351569 are the sum of divisors of the largest unitary divisor of n that is a square, and of the largest unitary divisor of n that is an exponentially odd number, respectively.

52, 98, 156, 164, 245, 260, 294, 332, 338, 364, 388, 392, 468, 490, 492, 539, 556, 572, 668, 722, 724, 735, 780, 820, 833, 845, 882, 884, 892, 927, 972, 976, 980, 988, 996, 1004, 1014, 1078, 1092, 1125, 1127, 1148, 1164, 1172, 1176, 1196, 1228, 1274, 1300, 1352, 1396, 1404, 1421, 1470, 1476, 1508, 1525, 1568, 1573

Offset: 1

Antti Karttunen, Nov 15 2024

nonn

			A351568(52) = 7 and A351569(52) = 14, so they share a factor (7), and therefore 52 is included as a term.

Antti Karttunen, Table of n, a(n) for n = 1..10000
Index entries for sequences related to sigma(n)

Positions k where A377990(k) is larger than A051027(k).
Cf. A350388, A350389, A351568, A351569.
Subsequence of A336548.

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); };
A351568(n) = sigma(A350388(n));
isA377991(n) = (1A351568(n), sigma(n)/A351568(n)));

{k such that gcd(A351568(n),A351569(n)) > 1}.

{k such that A377990(k) > A051027(k)}.

cp's OEIS Frontend

A377991 Numbers k such that A351568(k) and A351569(k) are not coprime, where A351568 and A351569 are the sum of divisors of the largest unitary divisor of n that is a square, and of the largest unitary divisor of n that is an exponentially odd number, respectively.

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