This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A032350 Palindromic nonprime numbers. 15
 1, 4, 6, 8, 9, 22, 33, 44, 55, 66, 77, 88, 99, 111, 121, 141, 161, 171, 202, 212, 222, 232, 242, 252, 262, 272, 282, 292, 303, 323, 333, 343, 363, 393, 404, 414, 424, 434, 444, 454, 464, 474, 484, 494, 505, 515, 525, 535, 545, 555, 565, 575, 585, 595, 606, 616 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Complement of A002385 (palindromic primes) with respect to A002113 (palindromic numbers). Union of A222724, A043047 (without number 2), A222726, A043039, A043040 (without number 5), A043041, A222728, A043043 and A222729. - Jaroslav Krizek, Mar 12 2013 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 LINKS Jaroslav Krizek, Table of n, a(n) for n = 1..10217 W. D. Banks, D. N. Hart, M. Sakata, Almost all palindromes are composite, Math. Res. Lett., 11 No. 5-6 (2004), 853-868. P. De Geest, World!Of Numbers P. De Geest, World!Of Palindromic Primes MATHEMATICA palq[n_] := IntegerDigits[n]==Reverse[IntegerDigits[n]]; Select[Range[700], palq[ # ]&&!PrimeQ[ # ]&] (* Second program: *) Select[Range@ 616, And[PalindromeQ@ #, ! PrimeQ@ #] &] (* Michael De Vlieger, Jan 02 2018 *) PROG (Sage) [n for n in (1..616) if not is_prime(n) and Word(n.digits()).is_palindrome()] # Peter Luschny, Sep 13 2018 (GAP) Filtered([1..620], n-> not IsPrime(n) and ListOfDigits(n)=Reversed(ListOfDigits(n))); # Muniru A Asiru, Mar 08 2019 CROSSREFS Cf. A002385. Sequence in context: A267509 A162738 A161600 * A078337 A046351 A161732 Adjacent sequences:  A032347 A032348 A032349 * A032351 A032352 A032353 KEYWORD easy,nonn,base AUTHOR EXTENSIONS Edited by Dean Hickerson, Oct 22 2002 STATUS approved

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

Last modified October 18 13:59 EDT 2019. Contains 328161 sequences. (Running on oeis4.)