

A046523


Smallest number with same prime signature as n.


210



1, 2, 2, 4, 2, 6, 2, 8, 4, 6, 2, 12, 2, 6, 6, 16, 2, 12, 2, 12, 6, 6, 2, 24, 4, 6, 8, 12, 2, 30, 2, 32, 6, 6, 6, 36, 2, 6, 6, 24, 2, 30, 2, 12, 12, 6, 2, 48, 4, 12, 6, 12, 2, 24, 6, 24, 6, 6, 2, 60, 2, 6, 12, 64, 6, 30, 2, 12, 6, 30, 2, 72, 2, 6, 12, 12, 6, 30, 2, 48, 16, 6, 2, 60, 6, 6, 6, 24, 2
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OFFSET

1,2


LINKS

T. D. Noe, Table of n, a(n) for n = 1..10000


FORMULA

In prime factorization of n, replace most common prime by 2, next most common by 3, etc.
a(n) = A124859(A124859(n)) = A181822(A124859(n)).  Matthew Vandermast, May 19 2012


EXAMPLE

If p,q,.. are different primes, a(p)=2, a(p^2)=4, a(pq)=6, a(p^2*q)=12, etc.
n = 108 = 2.2.3.3.3 is replaced by a(n) = 2.2.2.3.3 = 72;
n = 105875 = 5.5.5.7.11.11 is represented by a(n) = 2.2.2.3.3.5 = 360.
Primepowers are replaced by corresponding powers of 2, primes by 2.
Factorials, primorials and LCM[1,..,n] are in the sequence.
A000005(a(n)) = A000005(n) remains invariant; least and largest prime factors of a(n) are 2 or p[A001221(n)] resp.


MAPLE

a:= n> (l> mul(ithprime(i)^l[i][2], i=1..nops(l)))
(sort(ifactors(n)[2], (x, y)>x[2]>y[2])):
seq(a(n), n=1..100); # Alois P. Heinz, Aug 18 2014


MATHEMATICA

Table[Apply[Times, p[w]^Reverse[Sort[ex[w]]]], {w, 1, 1000}] p[x_] := Table[Prime[w], {w, 1, lf[x]}] ex[x_] := Table[Part[ffi[x], 2*w], {w, 1, lf[x]}] ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]]
ps[n_] := Sort[Last /@ FactorInteger[n]]; Join[{1}, Table[i = 2; While[ps[n] != ps[i], i++]; i, {n, 2, 89}]] (* Jayanta Basu, Jun 27 2013 *)


PROG

(PARI) a(n)=my(f=vecsort(factor(n)[, 2], , 4), p); prod(i=1, #f, (p=nextprime(p+1))^f[i]) \\ Charles R Greathouse IV, Aug 17 2011
(Haskell)
import Data.List (sort)
a046523 = product .
zipWith (^) a000040_list . reverse . sort . a124010_row
 Reinhard Zumkeller, Apr 27 2013
(Python)
from sympy import factorint
def P(n):
f = factorint(n)
return sorted([f[i] for i in f])
def a(n):
x=1
while True:
if P(n) == P(x): return x
else: x+=1 # Indranil Ghosh, May 05 2017


CROSSREFS

A025487 gives range of values of this sequence.
Cf. A000142, A002110, A003418, A001221, A000040, A000005, A124010, A071364, A085079, A089247.
Sequence in context: A083260 A284011 A275468 * A278524 A278523 A071364
Adjacent sequences: A046520 A046521 A046522 * A046524 A046525 A046526


KEYWORD

nonn,easy,nice


AUTHOR

N. J. A. Sloane.


EXTENSIONS

Corrected and extended by Ray Chandler, Mar 11 2004


STATUS

approved



