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A032350 Palindromic nonprime numbers.

%I A032350 #41 Apr 07 2021 14:40:05
%S A032350 1,4,6,8,9,22,33,44,55,66,77,88,99,111,121,141,161,171,202,212,222,
%T A032350 232,242,252,262,272,282,292,303,323,333,343,363,393,404,414,424,434,
%U A032350 444,454,464,474,484,494,505,515,525,535,545,555,565,575,585,595,606,616
%N A032350 Palindromic nonprime numbers.
%C A032350 Complement of A002385 (palindromic primes) with respect to A002113 (palindromic numbers). - _Jaroslav Krizek_, Mar 12 2013
%C A032350 Banks, Hart, and Sakata derive a nontrivial upper bound for the number of prime palindromes n <= x as x tends to infinity. It follows that almost all palindromes are composite. The results hold in any base. The authors use Weil's bound for Kloosterman sums. - _Jonathan Sondow_, Jan 02 2018
%H A032350 Georg Fischer, <a href="/A032350/b032350.txt">Table of n, a(n) for n = 1..10217</a>
%H A032350 W. D. Banks, D. N. Hart, and M. Sakata, <a href="http://dx.doi.org/10.4310/MRL.2004.v11.n6.a10">Almost all palindromes are composite</a>, Math. Res. Lett., 11 No. 5-6 (2004), 853-868.
%H A032350 Patrick De Geest, <a href="http://www.worldofnumbers.com/index.html">World!Of Numbers</a>
%H A032350 Patrick De Geest, <a href="http://www.worldofnumbers.com/palpri.htm">World!Of Palindromic Primes</a>
%t A032350 palq[n_] := IntegerDigits[n]==Reverse[IntegerDigits[n]]; Select[Range[700], palq[ # ]&&!PrimeQ[ # ]&]
%t A032350 (* Second program: *)
%t A032350 Select[Range@ 616, And[PalindromeQ@ #, ! PrimeQ@ #] &] (* _Michael De Vlieger_, Jan 02 2018 *)
%o A032350 (Sage)
%o A032350 [n for n in (1..616) if not is_prime(n) and Word(n.digits()).is_palindrome()] # _Peter Luschny_, Sep 13 2018
%o A032350 (GAP) Filtered([1..620],n-> not IsPrime(n) and ListOfDigits(n)=Reversed(ListOfDigits(n))); # _Muniru A Asiru_, Mar 08 2019
%Y A032350 Cf. A002113, A002385.
%K A032350 easy,nonn,base
%O A032350 1,2
%A A032350 _Patrick De Geest_
%E A032350 Edited by _Dean Hickerson_, Oct 22 2002