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 A053178 Numbers ending in 1 which are not prime. 1
 1, 21, 51, 81, 91, 111, 121, 141, 161, 171, 201, 221, 231, 261, 291, 301, 321, 341, 351, 361, 371, 381, 391, 411, 441, 451, 471, 481, 501, 511, 531, 551, 561, 581, 591, 611, 621, 651, 671, 681, 711, 721, 731, 741, 771, 781, 791, 801, 831, 841, 851, 861, 871 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Nonprime numbers of the form k*10+1. - Juri-Stepan Gerasimov, Oct 14 2009 LINKS Table of n, a(n) for n=1..53. EXAMPLE a(4) = 91 may look prime to some, but is composite. MAPLE remove(isprime, [10*j+1\$j=0..99])[]; # Alois P. Heinz, Jan 21 2021 PROG (PARI) isok(n) = ((n % 10) == 1) && (! isprime(n)) \\ Michel Marcus, Jul 26 2013 (Python) from sympy import isprime def aupto(lim): return [m for m in range(1, lim+1, 10) if not isprime(m)] print(aupto(871)) # Michael S. Branicky, Jan 21 2021 CROSSREFS Cf. A002808, A017281, A153275. Sequence in context: A153441 A357679 A235884 * A166150 A224334 A305002 Adjacent sequences: A053175 A053176 A053177 * A053179 A053180 A053181 KEYWORD easy,nonn,base AUTHOR Enoch Haga, Feb 29 2000 STATUS approved

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Last modified September 10 20:00 EDT 2024. Contains 375794 sequences. (Running on oeis4.)