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A046452 Concatenation of the 3 prime factors of a(n) is a palindrome. 4
8, 27, 125, 343, 429, 507, 795, 1309, 1331, 1533, 1547, 1587, 2023, 2097, 3633, 3729, 3897, 5289, 5295, 5547, 6597, 7833, 8029, 8427, 9583, 9795, 12207, 12795, 13489, 13573, 14133, 14147, 14295, 15463, 15549, 15987, 16233, 17295, 20667, 22139, 28273, 28609, 28847, 28951 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence is the intersection of A046447 and A014612 without the initial term. - Charles R Greathouse IV, Apr 23 2010

Apart from a(1) all terms are odd. Apart from a(3) 5 divides a(n) if and only if 15 divides a(n). - Charles R Greathouse IV, Jan 04 2013

LINKS

Robert Israel, Table of n, a(n) for n = 1..2292

EXAMPLE

14133 = 3 * 7 * 673 -> 37673 is palindromic.

MAPLE

Nmax:= 10000; # to get all a(n) <= Nmax

R:= {8}:

for i from 2 do

   a:= ithprime(i);

   if a^3 > Nmax then break end if;

   m:= length(a); tm:= 10^m;

   al:= convert(a, base, 10);

   ar:= add(10^(m-k)*al[k], k=1..m);

   for j from i  do

     b:= ithprime(j);

     if a*b^2 > Nmax then break end if;

     bl:= convert(b, base, 10);

     k0:= ceil((b-ar)/tm);

     for k from k0 do

       c:= ar + k*tm;

       if a*b*c > Nmax then break end if;

       if not isprime(c) then next end if;

       L:= [op(convert(c, base, 10)), op(bl), op(al)];

       if ListTools:-Reverse(L)=L then

         R:= R union {a*b*c}

       end if;

     end do

   end do

end do:

R;  # Robert Israel, Jan 05 2013

MATHEMATICA

pfpQ[n_]:=Module[{c=Flatten[IntegerDigits/@Table[#[[1]], {#[[2]]}]&/@ FactorInteger[ n]]}, c==Reverse[c]]; Select[Range[30000], PrimeOmega[#] == 3&&pfpQ[#]&] (* Harvey P. Dale, Jan 05 2013 *)

PROG

(PARI) ispal(n)=n=digits(n); for(i=1, #n\2, if(n[i]!=n[#n+1-i], return(0))); 1

list(lim)=my(v=List([8]), t); forprime(p=3, lim\9, forprime(q=3, min(lim\(3*p), p), t=p*q; forprime(r=3, min(lim\t, q), if(ispal(eval(Str(r, q, p))), listput(v, t*r))))); vecsort(Vec(v)) \\ Charles R Greathouse IV, Jan 04 2013

CROSSREFS

Cf. A046447.

Sequence in context: A062838 A240859 A277047 * A030078 A051751 A133042

Adjacent sequences:  A046449 A046450 A046451 * A046453 A046454 A046455

KEYWORD

nonn,base

AUTHOR

Patrick De Geest, Jul 15 1998.

EXTENSIONS

Missing a(16) from Charles R Greathouse IV on the advice of Harvey P. Dale, Jan 04 2013

STATUS

approved

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Last modified May 30 06:51 EDT 2017. Contains 287302 sequences.