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 A173288 Either n^2+n+{1,9} is prime. 1
 2, 3, 4, 5, 6, 8, 12, 13, 14, 15, 16, 17, 19, 20, 21, 24, 25, 27, 28, 33, 38, 41, 43, 49, 50, 54, 55, 57, 59, 62, 66, 69, 71, 75, 76, 77, 78, 79, 80, 88, 89, 90, 99, 101, 105, 106, 110, 111, 117, 118, 119, 121, 131, 138, 139, 141, 143, 145, 147, 150, 151, 153, 154, 155 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Or numbers n such that either n-th oblong number plus 1 or 9 is prime. Numbers n such that n^2+n+1 or n^2+n+9 is prime, but not both. [From R. J. Mathar, Feb 21 2010] LINKS EXAMPLE a(1)=1 because 1^2+1+1=4=nonprime and 1^2+1+9=11=prime; a(2)=2 because 2^2+2+1=7=prime and 2^2+2+9=15=nonprime; a(3)=3 because 3^2+3+1=13=prime and 3^3+3+9=21=nonprime. MATHEMATICA Select[Range, Xor@@PrimeQ[#^2+#+{1, 9}]&] (* Harvey P. Dale, Apr 26 2013 *) CROSSREFS Cf. A000040, A002378. Sequence in context: A181324 A050933 A103302 * A134677 A104419 A092232 Adjacent sequences:  A173285 A173286 A173287 * A173289 A173290 A173291 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Feb 15 2010 EXTENSIONS 1 and 11 removed by R. J. Mathar, Feb 21 2010 STATUS approved

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Last modified August 12 17:17 EDT 2020. Contains 336439 sequences. (Running on oeis4.)