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 A091113 Nonprimes of the form 4*k+1. 13
 1, 9, 21, 25, 33, 45, 49, 57, 65, 69, 77, 81, 85, 93, 105, 117, 121, 125, 129, 133, 141, 145, 153, 161, 165, 169, 177, 185, 189, 201, 205, 209, 213, 217, 221, 225, 237, 245, 249, 253, 261, 265, 273, 285, 289, 297, 301, 305, 309, 321, 325, 329, 333, 341, 345 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Muniru A Asiru, Table of n, a(n) for n = 1..10000 MAPLE A091113 := proc(n)     option remember;     if n =1 then         1;     else         for a from procname(n-1)+4 by 4 do             if not isprime(a) then                 return a;             end if;         end do:     end if; end proc: seq(A091113(n), n=1..100) ; # R. J. Mathar, Aug 29 2018 MATHEMATICA Do[If[ !PrimeQ[n]&&Equal[Mod[n, 4], 1], Print[n]], {n, 1, 1000}] Select[4*Range[0, 100]+1, !PrimeQ[#]&] (* Harvey P. Dale, Oct 28 2017 *) PROG (GAP) Filtered(List([0..100], k->4*k+1), n->not IsPrime(n)); # Muniru A Asiru, Mar 10 2019 (MAGMA) [n: n in [1..350] | IsIntegral((n-1)/4) and not IsPrime(n)]; // G. C. Greubel, Mar 10 2019 (Sage) [n for n in (1..350) if ((n-1)/4).is_integer() and not is_prime(n)] # G. C. Greubel, Mar 10 2019 (PARI) isok(n) = !isprime(n) && !((n-1) % 4); \\ Michel Marcus, Mar 11 2019 CROSSREFS Cf. A091236, A014076. Subsequence of A016813 (4*n+1). Sequence in context: A327756 A210251 A143791 * A188159 A272600 A327862 Adjacent sequences:  A091110 A091111 A091112 * A091114 A091115 A091116 KEYWORD nonn AUTHOR Labos Elemer, Feb 24 2004 STATUS approved

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Last modified April 5 10:20 EDT 2020. Contains 333239 sequences. (Running on oeis4.)