The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Please make a donation to keep the OEIS running. We are now in our 56th year. In the past year we added 10000 new sequences and reached almost 9000 citations (which often say "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A056561 Numbers n such that n^2 + n + 41 is prime. 23
 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 42, 43, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 64, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Among first 100000 terms, the only run of 13 subsequent values >39 is 219..231. - Zak Seidov, Jan 28 2009 Number of terms less than 10^n: 1, 10, 86, 581, 4149, 31985, 261081, 2208197, 19132652, ... . - Robert G. Wilson v, Apr 20 2015 Complement of A007634. - Robert Israel, Apr 20 2015 REFERENCES P. Hoffman, Archimedes' Revenge, pp. 39-40,Penguin Books 1988. LINKS Zak Seidov, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Euler Prime FORMULA a(n) = (sqrt(4*A005846(n)-163)-1)/2. a(n) = A002837(n+1)-1. - Robert Price, Nov 08 2019 EXAMPLE 39 is in the sequence because 39^2+39+41=1601 which is prime but 40 is not because 40^2+40+41=1681=41*41. MAPLE select(t -> isprime(t^2+t+41), [\$0..100]); # Robert Israel, Apr 20 2015 MATHEMATICA Select[Range[80], PrimeQ[#^2 + # + 41] &] (* Vincenzo Librandi, Sep 28 2012 *) PROG (MAGMA) [n: n in [0..80] |IsPrime(n^2 + n + 41)]; // Vincenzo Librandi, Sep 28 2012 (Haskell) a056561 n = a056561_list !! (n-1) a056561_list = filter ((== 1) . a010051' . a202018) [0..] -- Reinhard Zumkeller, Jul 03 2015 (PARI) is(n)=isprime(n^2+n+41) \\ Charles R Greathouse IV, Sep 02 2015 CROSSREFS Cf. A002837, A005846, A007634, A010051, A202018, A259645. Sequence in context: A083243 A002837 A271143 * A321993 A236674 A273886 Adjacent sequences:  A056558 A056559 A056560 * A056562 A056563 A056564 KEYWORD nonn,easy AUTHOR Henry Bottomley, Jun 26 2000 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified November 25 19:33 EST 2020. Contains 338625 sequences. (Running on oeis4.)