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 A296444 Numbers k such that 2*10^(2k)+2*10^k+1 are prime. 1
 2, 3, 6, 10, 276, 746, 1090, 1485, 6186 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers of this form divide 4*10^(4k)+1. LINKS EXAMPLE 20201, 2002001, 2000002000001, and 200000000020000000001 are prime, while 221=13*17, 200020001=569*351529, and 20000200001=17*29*1129*35933. MATHEMATICA ParallelMap[ If[ PrimeQ[2*10^(2 #) + 2*10^# + 1], #, Nothing] &, Range@ 6500] (* Robert G. Wilson v, Dec 13 2017 *) PROG (PARI) isok(k) = isprime(2*10^(2*k)+2*10^k+1); \\ Michel Marcus, Dec 13 2017 CROSSREFS See A296443 for 2*10^(2k)-2*10^k+1. Sequence in context: A056606 A186408 A062527 * A038752 A125714 A247953 Adjacent sequences:  A296441 A296442 A296443 * A296445 A296446 A296447 KEYWORD nonn,more AUTHOR Patrick A. Thomas, Dec 13 2017 EXTENSIONS a(5)-a(6) from Michel Marcus, Dec 13 2017 a(7)-a(9) from Robert G. Wilson v, Dec 13 2017 STATUS approved

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Last modified June 18 07:06 EDT 2019. Contains 324203 sequences. (Running on oeis4.)