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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

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

Patrick De Geest

EXTENSIONS

Edited by Dean Hickerson, Oct 22 2002

STATUS

approved

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Last modified December 14 18:21 EST 2018. Contains 318106 sequences. (Running on oeis4.)