A134156 a(n) = 2*tau(n) - n, where tau(n) is the number of divisors of n (A000005).

1, 2, 1, 2, -1, 2, -3, 0, -3, -2, -7, 0, -9, -6, -7, -6, -13, -6, -15, -8, -13, -14, -19, -8, -19, -18, -19, -16, -25, -14, -27, -20, -25, -26, -27, -18, -33, -30, -31, -24, -37, -26, -39, -32, -33, -38, -43, -28, -43, -38, -43, -40, -49, -38, -47, -40, -49, -50, -55, -36

Offset: 1

Author

Paul Curtz, Jan 12 2008

Keywords

• sign
• easy

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000005 (tau), A049820.

Programs

PARI

a(n) = {2*numdiv(n) - n} \\ Andrew Howroyd, Feb 02 2020

Formula

a(n) = A000005(n) - A049820(n).

a(n) = n - 2*A049820(n). - Wesley Ivan Hurt, Feb 17 2024

Extensions

Offset corrected and terms a(21) and beyond from Andrew Howroyd, Feb 02 2020