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

Offset: 1

Author

Antti Karttunen, Jul 11 2024

Keywords

• nonn
• more

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.

Examples

			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.
		

Crossrefs

Cf. A000203, A000265, A064989, A161942, A347391, A374464.

Programs

PARI

isA374463(n) = (A000265(sigma(n)==A000265(A064989(n))));

Formula

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