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A243103 Product of numbers m with 2 <= m <= n whose prime divisors all divide n. 7
1, 2, 3, 8, 5, 144, 7, 64, 27, 3200, 11, 124416, 13, 6272, 2025, 1024, 17, 35831808, 19, 1024000, 3969, 247808, 23, 859963392, 125, 346112, 729, 2809856, 29, 261213880320000000, 31, 32768, 264627, 18939904, 30625, 26748301344768, 37, 23658496, 369603, 32768000000, 41 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This sequence is the product of n-regular numbers.

A number m is said to be "regular" to n or "n-regular" if all the prime factors p of m also divide n.

The divisor is a special case of a regular m such that m also divides n in addition to all of its prime factors p | n.

Analogous to A007955 (Product of divisors of n).

If n is 1 or prime, a(n) = n.

If n is a prime power, a(n) = A007955(n).

Note: b-file ends at n = 4619, because a(4620) has more than 1000 decimal digits.

Product of the numbers 1 <= k <= n such that (floor(n^k/k) - floor((n^k - 1)/k)) = 1. - Michael De Vlieger, May 26 2016

LINKS

Michael De Vlieger, Table of n, a(n) for n = 1..4619

Encyclopedia Britannica, Regular Number (base-neutral definition)

Eric W. Weisstein, Regular Number (decimal definition)

Wikipedia, Regular Number (sexagesimal / Hamming number definition)

FORMULA

a(n) = product of terms of n-th row of irregular triangle A162306(n,k).

a(n) = Product_{k=1..n} k^( floor(n^k/k)-floor((n^k -1)/k) ). - Anthony Browne, Jul 06 2016

From Antti Karttunen, Mar 22 2017: (Start)

a(n) = Product_{k=2..n, A123275(n,k)=1} k.

For n >= 1, A046523(a(n)) = A283990(n).

(End)

EXAMPLE

a(12) = 124416 since 1 * 2 * 3 * 4 * 6 * 8 * 9 * 12 = 124416. These numbers are products of prime factors that are the distinct prime divisors of 12 = {2, 3}.

From David A. Corneth, Feb 09 2015: (Start)

Let p# be the product of primes up to p, A002110. Then

a(13#) ~= 8.3069582 * 10 ^ 4133

a(17#) ~= 1.3953000 * 10 ^ 22689

a(19#) ~= 3.8258936 * 10 ^ 117373

a(23#) ~= 6.7960327 * 10 ^ 594048

a(29#) ~= 1.3276817 * 10 ^ 2983168

a(31#) ~= 2.8152792 * 10 ^ 14493041

a(37#) ~= 1.9753840 * 10 ^ 69927040

Up to n = 11# already in the table.

(End)

MAPLE

A:= proc(n) local F, S, s, j, p;

  F:= numtheory:-factorset(n);

  S:= {1};

  for p in F do

    S:= {seq(seq(s*p^j, j=0..floor(log[p](n/s))), s=S)}

  od;

  convert(S, `*`)

end proc:

seq(A(n), n=1..100); # Robert Israel, Feb 09 2015

MATHEMATICA

regularQ[m_Integer, n_Integer] := Module[{omega = First /@ FactorInteger @ m }, If[Length[Select[omega, Divisible[n, #] &]] == Length[omega], True, False]]; a20140819[n_Integer] := Times @@ Flatten[Position[Thread[regularQ[Range[1, n], n]], True]]; a20140819 /@ Range[41]

regulars[n_] := Block[{f, a}, f[x_] := First /@ FactorInteger@ x; a = f[n]; {1}~Join~Select[Range@ n, SubsetQ[a, f@ #] &]]; Array[Times @@ regulars@ # &, 12] (* Michael De Vlieger, Feb 09 2015 *)

Table[Times @@ Select[Range@ n, (Floor[n^#/#] - Floor[(n^# - 1)/#]) == 1 &], {n, 41}] (* Michael De Vlieger, May 26 2016 *)

PROG

(PARI) lista(nn) = {vf = vector(nn, n, Set(factor(n)[, 1])); vector(nn, n, prod(i=1, n, if (setintersect(vf[i], vf[n]) == vf[i], i, 1))); } \\ Michel Marcus, Aug 23 2014

(PARI) for(n=1, 100, print1(prod(k=1, n, k^(floor(n^k/k) - floor((n^k - 1)/k))), ", ")) \\ Indranil Ghosh, Mar 22 2017

(Python)

from sympy import primefactors

def A243103(n):

    y, pf = 1, set(primefactors(n))

    for m in range(2, n+1):

        if set(primefactors(m)) <= pf:

            y *= m

    return y # Chai Wah Wu, Aug 28 2014

(Scheme)

;; A naive implementation, code for A123275bi given under A123275:

(define (A243103 n) (let loop ((k n) (m 1)) (cond ((= 1 k) m) ((= 1 (A123275bi n k)) (loop (- k 1) (* m k))) (else (loop (- k 1) m)))))

;; Antti Karttunen, Mar 22 2017

CROSSREFS

Cf. A162306 (irregular triangle of regular numbers of n), A010846 (number of regular numbers of n), A244974 (sum of regular numbers of n), A007955, A244052 (record transform of regular numbers of n).

Cf. A123275, A283990.

Sequence in context: A136182 A170911 A067911 * A051696 A066570 A073656

Adjacent sequences:  A243100 A243101 A243102 * A243104 A243105 A243106

KEYWORD

nonn

AUTHOR

Michael De Vlieger, Aug 19 2014

STATUS

approved

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Last modified December 13 00:17 EST 2017. Contains 295954 sequences.