This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A290810 Numbers n such that 6n-1, 12n-1 and 18n-1 are all primes. 1
 1, 4, 5, 14, 15, 29, 39, 40, 49, 70, 110, 159, 169, 204, 235, 260, 264, 315, 334, 355, 390, 425, 449, 490, 560, 565, 599, 634, 725, 729, 735, 820, 824, 889, 1019, 1029, 1349, 1379, 1419, 1510, 1580, 1590, 1694, 1719, 1765, 1925, 1930, 1950, 1985, 2044, 2150 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS If n is in the sequence then (6n-1)(12n-1)(18n-1) = 36n * (36n^2 - 11n + 1) - 1 is a Lucas-Carmichael number (A006972). Analogous to A046025 as A006972 (Lucas-Carmichael numbers) is analogous to A002997 (Carmichael numbers). LINKS FORMULA 6*a(n) - 1 = A067256(n+1). EXAMPLE 1 is in the sequence since 6*1 - 1 = 5, 12*1 - 1 = 11 and 18*1 - 1 = 17 are all primes, and 5*11*17 = 935 is a Lucas-Carmichael number. MATHEMATICA seq = {}; Do[ If[ AllTrue[{6 m - 1, 12 m - 1, 18 m - 1}, PrimeQ ], AppendTo[seq, m] ], {m, 1, 10^5} ]; seq PROG (PARI) isok(n) = isprime(6*n-1) && isprime(12*n-1) && isprime(18*n-1); \\ Michel Marcus, Aug 11 2017 CROSSREFS Cf. A002997, A006972, A046025, A067256, A087788, A216925. Intersection of A024898, A138620 and A138918. Sequence in context: A238315 A091311 A008540 * A000867 A191142 A049770 Adjacent sequences:  A290807 A290808 A290809 * A290811 A290812 A290813 KEYWORD nonn AUTHOR Amiram Eldar, Aug 11 2017 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 October 23 23:51 EDT 2019. Contains 328379 sequences. (Running on oeis4.)