A258468 a(n) = lcm(n, n - tau(n)).

0, 0, 3, 4, 15, 6, 35, 8, 18, 30, 99, 12, 143, 70, 165, 176, 255, 36, 323, 140, 357, 198, 483, 48, 550, 286, 621, 308, 783, 330, 899, 416, 957, 510, 1085, 108, 1295, 646, 1365, 160, 1599, 714, 1763, 836, 585, 966, 2115, 912, 2254, 1100, 2397, 1196

Offset: 1

Author

Carlos Eduardo Olivieri, May 31 2015

Keywords

• nonn
• easy

Comments

For tau see A000005.

Examples

			a(5) = 15, since tau(5) = 2, lcm(5, 3) = 15.
a(7) = 35, since tau(7) = 2, lcm(7, 5) = 35.
a(10) = 30, since tau(10) = 4, lcm (10, 6) = 30.
		

Links

• Joshua Zelinsky, Tau Numbers: A Partial Proof of a Conjecture and Other Results, Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.8.

Crossrefs

Cf. A000005, A009230, A005563.

Programs

Mathematica

Table[LCM[n, n - DivisorSigma[0, n]], {n, 200}]

PARI

vector(100, n, lcm(n, n-numdiv(n))) \\ Michel Marcus, May 31 2015

Formula

a(n) = lcm(n, n - tau(n)).

a(n) = n * (n - 2) = A005563(n-2) if n is prime.

Extensions

Edited by Wolfdieter Lang, Jun 16 2015