login
This site is supported by donations to The OEIS Foundation.
Logo

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A131904 Smallest positive integer k with the same number of divisors as the n-th integer for which such a k exists. 0
2, 2, 2, 6, 4, 6, 2, 2, 6, 6, 2, 12, 2, 12, 6, 6, 2, 4, 6, 6, 12, 2, 24, 2, 12, 6, 6, 6, 2, 6, 6, 24, 2, 24, 2, 12, 12, 6, 2, 4, 12, 6, 12, 2, 24, 6, 24, 6, 6, 2, 2, 6, 12 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

FORMULA

a(n)=min(k>0, k has the same number of divisors as A131903(n))

EXAMPLE

a(4)=6 because A131903(n)=8 which has got four divisors and 6 is the least positive integer with four divisors

MATHEMATICA

Clear[tmp]; Function[n, If[Head[ #1] === tmp, #1 = n; Unevaluated[Sequence[]], # ] & [tmp[DivisorSigma[0, n]]]] /@ Range[64]

CROSSREFS

Cf. A069822, A131902-A131908.

Sequence in context: A084867 A194949 A099259 * A038074 A059885 A145890

Adjacent sequences:  A131901 A131902 A131903 * A131905 A131906 A131907

KEYWORD

easy,nonn

AUTHOR

Peter Pein (petsie(AT)dordos.net), Jul 26 2007

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 15 09:12 EST 2012. Contains 205749 sequences.