A192203 -id:A192203 - cp's OEIS frontend

A242621 Start of the least triple of consecutive squarefree numbers each of which has exactly n distinct prime factors.

2, 33, 1309, 27962, 3323705, 296602730, 41704979953

Offset: 1

M. F. Hasler, May 18 2014

nonn

As the example of a(4)=27962 shows, "consecutive squarefree numbers" means consecutive elements of A005117, not necessarily consecutive integers that (additionally) are squarefree; this would be a more restrictive condition.

a(8) <= 102099792179229 because A093550 - 1 is an upper bound of the present sequence.

			The two squarefree numbers following a(4)=27962, namely, 27965 and 27966, also have 4 prime divisors just as a(4).

Daniel C. Mayer, Define an "m-triple" to consist of three consecutive squarefree positive integers, each with exactly m prime divisors, Number Theory group on LinkedIn.com

See A242605-A242608 for triples of consecutive squarefree numbers with m=2,..,5 prime factors.
See A246470 for the quadruplet and A246548 for the 5-tuple versions of this sequence.
See A039833, A066509, A176167 and A192203 for triples of consecutive numbers which are squarefree and have m=2,..,5 prime factors.

Edited and a(6)-a(7) added by Hans Havermann, Aug 27 2014

A248204 Middle values in trios of products of 5 distinct primes.

Original entry on oeis.org

16467034, 18185870, 21134554, 21374354, 21871366, 22247554, 22412534, 22721586, 24845314, 25118094, 25228930, 25435334, 25596934, 26217246, 27140114, 29218630, 29752346, 30323734, 30563246, 31943066, 32663266, 33367894, 36055046, 38269022, 39738062, 40547066

Offset: 1

James G. Merickel, Oct 28 2014

nonn

A subsequence of A066509 and offset by 1 from A192203.

			16467033=3*11*17*149*197,
16467034=2*19*23*83*227, and
16467035=5*13*37*41*167,
with no smaller similar trio. So a(1)=16467034. [Corrected by _James G. Merickel_, Jul 23 2015]

James G. Merickel, Table of n, a(n) for n = 1..26

Cf. A066509, A192203, A248201, A248202, A248203, A259349, A259350, A259801.

{
\\ This program checks all consecutives with elements not divisible \\
\\ by the squares of 2 or 3. More efficiency is required if enormous \\
\\ numbers of terms are sought and for the analog sequences beyond \\
\\ 6 prime factors. The start value is A093550(5). If a start other \\
\\ than this is chosen, one must be sure that (one of) s or u is \\
\\ adjusted if it needs to be. \\
n=16467034;s=[8,4,4,4,8,8];u=1;
while(1,
  if(issquarefree(n) && issquarefree(n-1) && issquarefree(n+1) && omega(n)==5 && omega(n-1)==5 && omega(n+1)==5, print1(n" "));
  n+=s[u];
  if(u==6,u=1,u++)
)
} \\ James G. Merickel, Jul 23 2015

a(n) = A192203(n) + 1.

A364266 The first term in a chain of at least 3 consecutive numbers each with exactly 5 distinct prime factors.

Original entry on oeis.org

1042404, 3460280, 3818828, 3998664, 4638984, 4991964, 5540248, 5701254, 5715500, 5964958, 6772050, 6794084, 7237384, 7453964, 7459088, 7745318, 7757034, 7993194, 8083634, 8153430, 8168194, 8273628, 8340834, 8340980, 8414756, 8486994, 8698898, 8722634, 8758904

Offset: 1

R. J. Mathar, Jul 16 2023

nonn

			1042404 = 2^2*3*11*53*149, 1042405 = 5*6*143*29*79 and 1042406 = 2*17*23*31*43 each have 5 distinct prime factors, so 1042404 is in the sequence.

David A. Corneth, Table of n, a(n) for n = 1..10000

Cf. A192203 (subsequence for squarefree triples). Subsequence of A140079 (2 consec.) and of A006073.

Cf. A364308 (3 dist. factors), A364309 (4 dist. factors), A364265 (6 dist. factors), A001221, A087978.

omega := proc(n)
    nops(numtheory[factorset](n)) ;
end proc:
for k from 1 do
    if omega(k) = 5 then
        if omega(k+1) = 5 then
            if omega(k+2) = 5 then
                print(k) ;
            end if;
        end if;
    end if;
end do:

seq[lim_] := Module[{s  = {}, q1 = False, q2 = False, q3}, Do[q3 = PrimeNu[k] == 5; If[q1 && q2 && q3, AppendTo[s, k-2]]; q1 = q2; q2 = q3, {k, 3, lim}]; s]; seq[10^7] (* Amiram Eldar, Oct 01 2024 *)

a(1) = A087978(3).

{k: A001221(k) = A001221(k+1) = A001221(k+2) = 5}. - R. J. Mathar, Jul 18 2023

A242608 Start of a triple of consecutive squarefree numbers each of which has exactly 5 distinct prime factors.

Original entry on oeis.org

3323705, 3875934, 4393190, 4463822, 4929470, 5401626, 5654802, 6452535, 6465414, 6800934, 7427042, 7755890, 8233743, 8343906, 8406174, 8457942, 8593802, 8716323, 9186474, 9688382, 9812582, 9965415, 10364934, 10504074, 10870563, 10977834, 11460666, 11685894, 11993462, 12474602, 13151761

Offset: 1

M. F. Hasler, May 18 2014

nonn

See sequences A242605-A242607 (analog for m=2,3,4) for further information and examples; A242621 (first terms for positive m).

The definition of A192203 is more restrictive and therefore A192203 is a subsequence of this one, and A192203(1) >> A242608(1), roughly by a factor 5.

			a(1) = 3323705 = 5*7*11*89*97, a(1)+1 = 2*3*41*59*229 and a(1)+5 = 2*5*13*37*691 yield the first triple of consecutive squarefree numbers such that each of them is the product of five distinct primes.

Daniel C. Mayer, Define an "m-triple" to consist of three consecutive squarefree positive integers, each with exactly m prime divisors, Number Theory group on LinkedIn.com

(back(n)=for(i=1,2,until(issquarefree(n--),));n);for(n=10^6,2e7,issquarefree(n)||next;ndk==ndm&&ndk==5&&omega(n)==ndm&&print1(back(n)",");ndk=ndm;ndm=omega(n))

Minor edit by Hans Havermann, Aug 19 2014

A176167 First of a triple of consecutive integers, each the product of 4 distinct primes.

Original entry on oeis.org

203433, 214489, 225069, 258013, 294593, 313053, 315721, 352885, 389389, 409353, 418845, 421629, 452353, 464385, 478905, 485133, 500905, 508045, 508989, 526029, 528409, 538745, 542269, 542793, 548301, 556869, 559689, 569065, 571233, 579885

Offset: 1

Vladimir Joseph Stephan Orlovsky, Apr 10 2010

nonn

A subsequence of A242607 and A016813. - M. F. Hasler, May 19 2014

			203433 is a term: 203433 = 3*19*43*83, 203434 = 2*7*11*1321, 203435 = 5*23*29*61.

Zak Seidov, Table of n, a(n) for n = 1..1000

Cf. A039833, A066509, A192203. Subsequence of A140078 and of A318896.

f1[n_]:=Last/@FactorInteger[n]=={1,1,1,1};f2[n_]:=Max[Last/@FactorInteger[n]];lst={};Do[If[f1[n]&&f1[n+1]&&f1[n+2],AppendTo[lst,n]],{n,5*8!,7*9!}];lst

forstep(n=1+10^5,10^7,4, for(k=n,n+2,issquarefree(k)||next(2)); for(k=n,n+2,omega(k)==4||next(2));print1((n)",")) \\ M. F. Hasler, May 19 2014

A242492 For any integer m > 1, the m-th term of the sequence is the minimal squarefree integer x with exactly m prime divisors such that x+1 and x+2 are also squarefree integers with exactly m prime divisors.

Original entry on oeis.org

33, 1309, 203433, 16467033, 1990586013, 41704979953, 102099792179229

Offset: 2

Daniel Constantin Mayer, May 16 2014

The five terms for m = 2,3,4,5,6 were computed with the aid of PARI/GP. But it seems to be rather difficult to compute higher terms, if they exist at all.

The distribution of squarefree integers with exactly m prime factors is given in the book by Montgomery and Vaughan, Multiplicative Number Theory, but I do not have access to it and do not know whether it also addresses the problem of three consecutive numbers of this kind.

			33 = 3*11, 34 = 2*17, 35 = 5*7;
1309 = 7*11*17, 1310 = 2*5*131, 1311 = 3*19*23;
203433 = 3*19*43*83, 203434 = 2*7*11*1321, 203435 = 5*23*29*61;
16467033 = 3*11*17*149*197, 16467034 = 2*19*23*83*227, 16467035 = 5*13*37*41*167; (CPU time 48 seconds)
1990586013 = 3*13*29*67*109*241, 1990586014 = 2*23*37*43*59*461, 1990586015 = 5*11*17*19*89*1259. (CPU time 2 hours and 34 minutes)

Hugh L. Montgomery and Robert C. Vaughan: "Multiplicative Number Theory: 1. Classical Theory", Cambridge studies in advanced mathematics, vol. 97, Cambridge University Press (2007)

Math Overflow, Asymptotics of special square-free numbers, Mar 20 2014
Daniel Constantin Mayer, PARI/GP script "AdjacentSquareFree.gp"
Daniel Constantin Mayer, PARI/GP script "SquareFreeTriplets.gp"
Prime puzzles & problems connection, Square-free triples

Cf. A007675 (any m), A039833 (m=2), A066509 (m=3), A176167 (m=4), A192203 (m=5), A068088 (sextets with gap).

Cf. A242605-A242608 for start of triples of consecutive squarefree numbers with m=2,...,5 prime factors, A242621 for the analog of the present sequence in that spirit.

{default(primelimit,2M); lb=2; ub=2*10^9; m=1; i=0; j=0; loc=0; while(m<6, m=m+1; for(n=lb,ub, if(issquarefree(n)&&(m==omega(n)), loc=loc+1; if(1==loc, i=n; ); if(2==loc, if(i+1==n, j=n; ); if(i+1

a(n) = A093550(n)-1. - M. F. Hasler, May 20 2014

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A242621 Start of the least triple of consecutive squarefree numbers each of which has exactly n distinct prime factors.

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A248204 Middle values in trios of products of 5 distinct primes.

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A364266 The first term in a chain of at least 3 consecutive numbers each with exactly 5 distinct prime factors.

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A242608 Start of a triple of consecutive squarefree numbers each of which has exactly 5 distinct prime factors.

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A176167 First of a triple of consecutive integers, each the product of 4 distinct primes.

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A242492 For any integer m > 1, the m-th term of the sequence is the minimal squarefree integer x with exactly m prime divisors such that x+1 and x+2 are also squarefree integers with exactly m prime divisors.

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