This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A112041 Numbers k such that 1*k + 1, 3*k + 1, 9*k + 1, 27*k + 1 are all primes. 3
 4, 60, 180, 760, 910, 1020, 1230, 1600, 1860, 2160, 2280, 2440, 3850, 5800, 7320, 8680, 12940, 13780, 14740, 17350, 17400, 21840, 22720, 22960, 26040, 27010, 31050, 33870, 34060, 35200, 39900, 40030, 44350, 45280, 45540, 45750, 50460, 52050 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Conjecture: all terms except the first are multiples of 10. - Harvey P. Dale, Mar 26 2015 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE 1*4 + 1 = 5; 3*4 + 1 = 13; 9*4 + 1 = 37; 27*4 + 1 = 109; 5, 13, 37, 109 are all prime so 4 is in the sequence. MATHEMATICA Select[Range[60000], AllTrue[3^Range[0, 3]*#+1, PrimeQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, Mar 26 2015 *) PROG (MAGMA) [n: n in [1..100000] |IsPrime(n+1) and IsPrime(3*n+1) and IsPrime(9*n+1) and IsPrime(27*n+1)] // Vincenzo Librandi, Nov 13 2010 CROSSREFS Cf. A112042, A112043. Sequence in context: A074835 A060492 A234952 * A210425 A002060 A247739 Adjacent sequences:  A112038 A112039 A112040 * A112042 A112043 A112044 KEYWORD nonn AUTHOR Pierre CAMI, Aug 26 2005 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 12 07:17 EST 2018. Contains 318053 sequences. (Running on oeis4.)