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!)
 A241975 Numbers n such that n^4 - n^3 - n - 1 is a semiprime. 1
 4, 6, 10, 14, 16, 20, 36, 40, 54, 56, 66, 84, 90, 94, 116, 126, 146, 150, 156, 160, 170, 204, 210, 260, 264, 306, 340, 350, 386, 396, 406, 420, 464, 474, 496, 570, 634, 674, 696, 700, 716, 740, 764, 780, 816, 826, 864, 890, 966, 1054, 1070, 1094, 1106, 1144 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Since n^4 - n^3 - n - 1 = (n^2 + 1)*(n^2 - n - 1), these are also numbers n such that n^2 + 1 and n^2 - n - 1 are both prime. Numbers in the intersection of A005574 and A002328. - Derek Orr, Aug 10 2014 [Sequence numbers corrected by Jens Kruse Andersen, Aug 11 2014] LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..400 MATHEMATICA Select[Range[2000], PrimeOmega[#^4 - #^3 - # - 1]==2 &] PROG (MAGMA) IsSemiprime:=func; [ n: n in [2..1500] | IsSemiprime(n^4 - n^3 - n - 1)]; (PARI) for(n=1, 10^4, if(isprime(n^2+1)&&isprime(n^2-n-1), print1(n, ", "))) \\ Derek Orr, Aug 10 2014 CROSSREFS Cf. A001358, A002327, A002496, A085722, A241670, A243436. Sequence in context: A171945 A310583 A298784 * A063745 A123666 A095305 Adjacent sequences:  A241972 A241973 A241974 * A241976 A241977 A241978 KEYWORD nonn,less AUTHOR Vincenzo Librandi, Aug 10 2014 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 December 3 11:58 EST 2020. Contains 338900 sequences. (Running on oeis4.)