login
A101793
Primes of the form 16*k-1 such that 4*k-1 and 8*k-1 are also primes.
8
47, 719, 1439, 2879, 4079, 4127, 5807, 6047, 7247, 7727, 9839, 10799, 11279, 13967, 14159, 15647, 21599, 24527, 28319, 28607, 42767, 44687, 45887, 48479, 51599, 51839, 67247, 68639, 72767, 77279, 79967, 81647, 84047, 84719, 89087, 92399, 95279, 96959, 98207
OFFSET
1,1
LINKS
FORMULA
a(n) = 16*A101790(n) - 1 = 4*A101791(n) + 3 = 2*A101792(n) + 1. - Amiram Eldar, May 13 2024
EXAMPLE
4*3-1 = 11, 8*3-1 = 23 and 16*3-1 = 47 are primes, so 47 is a term.
MATHEMATICA
16#-1&/@Select[Range[10000], AllTrue[{4#-1, 8#-1, 16#-1}, PrimeQ]&] (* Harvey P. Dale, Jun 13 2015 *)
PROG
(PARI) is(k) = if(k % 16 == 15, my(m = k\16 + 1); isprime(4*m-1) && isprime(8*m-1) && isprime(16*m-1), 0); \\ Amiram Eldar, May 13 2024
CROSSREFS
Subsequence of A127576.
Subsequences: A101797, A101997.
Sequence in context: A106310 A163709 A244880 * A262120 A032626 A009054
KEYWORD
easy,nonn
AUTHOR
Douglas Stones (dssto1(AT)student.monash.edu.au), Dec 16 2004
STATUS
approved