1,2

a(n) <= n for all n. Moreover, a(n) = n if and only if n belongs to A005179.

Antti Karttunen, Table of n, a(n) for n = 1..10000

a(n) = A005179(A000005(n)).

(PARI) A140635(n) = { my(nd = numdiv(n)); for (i=1, n, if (numdiv(i) == nd, return (i))); }; \\ After A139770, Antti Karttunen, May 27 2017

(Python)

from sympy import divisor_count as d

def a(n):

x=d(n)

m=1

while True:

if d(m)==x: return m

else: m+=1 # Indranil Ghosh, May 27 2017

Cf. A000005, A005179, A139770.

Cf. A019505, A138113, A061300 (sequences that can be defined in terms of this sequence).

Sequence in context: A122457 A319410 A139770 * A283465 A283466 A270492

Adjacent sequences: A140632 A140633 A140634 * A140636 A140637 A140638

nonn

Max Alekseyev, May 19 2008

approved