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A066509 a(n) is the first of a triple of consecutive integers, each the product of three distinct primes. 13

%I

%S 1309,1885,2013,2665,3729,5133,6061,6213,6305,6477,6853,6985,7257,

%T 7953,8393,8533,8785,9213,9453,9821,9877,10281,10945,11605,12453,

%U 12565,12801,12857,12993,13053,14133,14313,14329,14465,14817,15085,15265,15805,16113,16133

%N a(n) is the first of a triple of consecutive integers, each the product of three distinct primes.

%C A subsequence of A052214 and thus of A005238. - _M. F. Hasler_, Jan 05 2013

%C Also, the start of pairs of adjacent sphenic twins, i.e., a(n) = A215217(k) such that A215217(k+1) = A215217(k)+1. Therefore these triples might be called "sphenic triples". They form a subsequence of A242606. - _M. F. Hasler_, May 18 2014

%H Harry J. Smith, <a href="/A066509/b066509.txt">Table of n, a(n) for n = 1..1000</a>

%H G. L. Honaker, Jr. and C. Caldwell, <a href="http://primes.utm.edu/curios/page.php?short=1309">Prime Curios!</a>

%e a(5) = 3729 because it along with 3730 and 3731 are all the product of three distinct primes.

%t f[n_]:=Last/@FactorInteger[n]=={1,1,1};lst={};Do[If[f[n]&&f[n+1]&&f[n+2],AppendTo[lst,n]],{n,9!}];lst (* _Vladimir Joseph Stephan Orlovsky_, Mar 04 2010 *)

%o (PARI) Trip(n) = { local(f); f=factor(n); if (matsize(f)[1] != 3, return(0)); for(i=1, 3, if (f[i, 2] != 1, return(0))); return(1); } { n=0; for (m=1, 10^10, if (!Trip(m) || !Trip(m+1) || !Trip(m+2), next); write("b066509.txt", n++, " ", m); if (n==1000, return) ) } \\ _Harry J. Smith_, Feb 19 2010

%o (PARI) A066509(n,show_all=0,a=2*3*5,s=[1,1,1]~)={until( !n-- || !a++, until(, factor(a+2)[,2]!=s && (a+=3) && next; factor(a+1)[,2]!=s && (a+=2) && next; factor(a)[,2]==s && break; factor(a+3)[,2]==s && a++ & break; a+=4);show_all&print1(a",")); a} \\ _M. F. Hasler_, Jan 05 2013

%o (PARI) is3dp(n)=my(f=factor(n));matsize(f)==[3,2]&&vecmax(f[,2])==1

%o list(lim)=my(v=List(),t);forprime(p=17,lim\15, forprime(q=7,min(p-1,lim\3), forprime(r=3,min(q-1,lim\(p*q)), t=p*q*r; if(t%4==1 && is3dp(t+1) && is3dp(t+2), listput(v,t))))); vecsort(Vec(v)) \\ _Charles R Greathouse IV_, Jan 05 2013

%K nonn

%O 1,1

%A _Jason Earls_, Jan 04 2002

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Last modified January 20 05:27 EST 2020. Contains 331067 sequences. (Running on oeis4.)