OFFSET
1,2
COMMENTS
If n is in the sequence then (6n+1)*(12n+1)*(18n+1) is a Carmichael number (A002997) and (6n-1)*(12n-1)*(18n-1) is a Lucas-Carmichael number (A006972).
The first 10 pairs of corresponding Lucas-Carmichael and Carmichael numbers ((6n-1)*(12n-1)*(18n-1), (6n+1)*(12n+1)*(18n+1)) are:
(935, 1729)
(921329139943799, 921392227198801)
(445860973748310119, 445864862313790921)
(451901165073782759, 451905088679976961)
(25715181770344848599, 25715239817629143601)
(58001133699332691839, 58001233533626759041)
(235803065459494289399, 235803319764534509401)
(843555229160685647759, 843555823997214441961)
(866240412591524160959, 866241018045184403161)
(1685504102154302331719, 1685505045798928055521)
(2416038446298343361039, 2416039645957333860241)
LINKS
Tim Johannes Ohrtmann, Table of n, a(n) for n = 1..10000
EXAMPLE
1 is in the sequence since (6*1 - 1, 6*1 + 1) = (5, 7), (12*1 - 1, 12*1 + 1) = (11, 13) and (18*1 - 1, 18*1 + 1) = (17, 19) are all pairs of twin primes.
MATHEMATICA
seq = {}; Do[ If[ AllTrue[{6 m - 1, 6 m + 1, 12 m - 1, 12 m + 1, 18 m - 1,
18 m + 1}, PrimeQ ], AppendTo[seq, m]], {m, 1, 10^7} ]; seq
Select[Range[6280000], AllTrue[{6#+1, 6#-1, 12#+1, 12#-1, 18#+1, 18#-1}, PrimeQ]&] (* Harvey P. Dale, Jun 21 2024 *)
PROG
(PARI) isok(n) = isprime(6*n-1) && isprime(6*n+1) && isprime(12*n-1) && isprime(12*n+1) && isprime(18*n-1) && isprime(18*n+1); \\ Michel Marcus, Aug 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Aug 11 2017
STATUS
approved