A227853 Numbers k such that 4620*k - 1 is a safe prime (A005385).

5, 9, 10, 20, 24, 39, 49, 50, 58, 67, 79, 88, 91, 97, 98, 103, 116, 117, 134, 136, 137, 143, 148, 149, 180, 181, 182, 193, 201, 213, 230, 234, 239, 247, 253, 261, 265, 267, 275, 284, 285, 286, 288, 296, 301, 304, 313, 321, 325, 339, 347

Offset

1,1

Comments

The given expression seems to produce safe primes quite frequently. The numbers 6*(4620*a(n)-1) form a subsequence of A230032.

Note that 4620 = 2^2*3*5*7*11.

Is a(4135..4139) = 59497..59501 the only set of 5 terms with common difference = 1? Checked for all terms up to 10^7. - Zak Seidov, Nov 02 2013

This is common because 4620 = 12*5*7*11 contains several small prime factors, which reduces the possible 12x-1 remainders, forcing all safe primes to be in other 12x-1 remainders mod 4620. Something similar would happen if 4620 were replaced with 12*5*7*13 = 5460. - Mark Andreas, Dec 31 2021

Links

Jon E. Schoenfield, Table of n, a(n) for n = 1..10000

Prog

(PARI) {f=4*3*5*7*11; for(k=1, 2000, isprime(p=k*f-1)&&isprime(p\2)&&print1(k", "))}

Crossrefs

Cf. A005385, A230032.

Sequence in context: A242139 A216765 A117771 * A275240 A175437 A119124

Adjacent sequences: A227850 A227851 A227852 * A227854 A227855 A227856

Keyword

nonn

Author

M. F. Hasler, Oct 31 2013

Status

approved