login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A033620 Numbers all of whose prime factors are palindromes. 7

%I

%S 1,2,3,4,5,6,7,8,9,10,11,12,14,15,16,18,20,21,22,24,25,27,28,30,32,33,

%T 35,36,40,42,44,45,48,49,50,54,55,56,60,63,64,66,70,72,75,77,80,81,84,

%U 88,90,96,98,99,100,101,105,108,110,112,120,121,125,126,128,131

%N Numbers all of whose prime factors are palindromes.

%C Multiplicative closure of A002385; A051038 and A046368 are subsequences. [_Reinhard Zumkeller_, Apr 11 2011]

%t palQ[n_]:=Reverse[x=IntegerDigits[n]]==x; Select[Range[131],And@@palQ/@First/@FactorInteger[#]&] (* _Jayanta Basu_, Jun 05 2013 *)

%o (Haskell)

%o a033620 n = a033620_list !! (n-1)

%o a033620_list = filter chi [1..] where

%o chi n = a136522 spf == 1 && (n' == 1 || chi n') where

%o n' = n `div` spf

%o spf = a020639 n -- cf. A020639

%o -- _Reinhard Zumkeller_, Apr 11 2011

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

%o is(n)=if(n<13,n>0,vecmin(apply(ispal,factor(n)[,1]))) \\ _Charles R Greathouse IV_, Feb 06 2013

%K nonn,base,easy

%O 1,2

%A _N. J. A. Sloane_, May 17 1998

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified July 25 15:47 EDT 2014. Contains 244915 sequences.