A374463 - OEIS

A374463

Numbers k such that the odd parts of sigma(k) and A064989(k) are equal, where A064989 shifts the prime factorization one step towards lower primes, and sigma is the sum of divisors function.

1, 3, 5, 15, 189, 945, 2125, 6375, 9261, 42550, 46305, 127650, 401625, 936100, 1191400, 2808300, 3574200, 8041950, 19679625, 22469750, 58378600, 58506250, 67409250, 175135800, 175518750, 176922900, 394055550, 494334500

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OFFSET

1,2

COMMENTS

Odd terms after 1 form a subsequence of A347391.

If x and y are included, and they are coprime (gcd(x,y) = 1), then x*y is also included.

LINKS

Table of n, a(n) for n=1..28.

FORMULA

{k | A000265(sigma(k)) = A000265(A064989(k))}.

EXAMPLE

945 = 3^3 * 5 * 7 is included as A064989(945) = 2^3 * 3 * 5 = 120, and sigma(945) = 1920 = 2^7 * 3 * 5, with A000265(120) = A000265(1920) = 15.