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 A174969 Composites of form n^2 + n + 1. 3
 21, 57, 91, 111, 133, 183, 273, 343, 381, 507, 553, 651, 703, 813, 871, 931, 993, 1057, 1191, 1261, 1333, 1407, 1561, 1641, 1807, 1893, 1981, 2071, 2163, 2257, 2353, 2451, 2653, 2757, 2863, 3081, 3193, 3423, 3661, 3783, 4033, 4161, 4291, 4557, 4693, 4971 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES L. Poletti, Le serie dei numeri primi appartenente alle due forme quadratiche (A) n^2+n+1 e (B) n^2+n-1 per l'intervallo compreso entro 121 milioni, e cioè per tutti i valori di n fino a 11000, Atti della Reale Accademia Nazionale dei Lincei, Memorie della Classe di Scienze Fisiche, Matematiche e Naturali, s. 6, v. 3 (1929), pages 193-218. LINKS C. K. Caldwell, Composite Numbers EXAMPLE n=1 gives 1^2+1+1=3, which is prime and so not a term, and similarly for n=2,3; n=4 gives 21=3*7, which is a(1). MAPLE with(numtheory):for n from 0 to 200 do:x:=n^2+n+1: if type(x, prime)=false then print (x):else fi:od: MATHEMATICA Select[Array[ #^2+#+1&, 6!, 2], !PrimeQ[ # ]&] (* Vladimir Joseph Stephan Orlovsky, Apr 07 2010 *) CROSSREFS Cf. A174967, A002384, A002383, A110284. Sequence in context: A280884 A257103 A146560 * A176069 A043382 A044123 Adjacent sequences:  A174966 A174967 A174968 * A174970 A174971 A174972 KEYWORD nonn AUTHOR Michel Lagneau, Apr 02 2010 EXTENSIONS Example edited and keyword uned removed by D. S. McNeil, Nov 17 2010 STATUS approved

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Last modified January 22 15:02 EST 2022. Contains 350481 sequences. (Running on oeis4.)