A265683 Numbers n such that 16^n * (16^n - 1) - 1 is prime.

1, 27, 52, 56, 60, 252, 270, 367, 390, 2154, 3247, 13444, 35724, 46917, 79236, 87324

Offset: 1

Author

Shivam N. Patel, Dec 13 2015

Keywords

• nonn
• more

Comments

Each of the corresponding numbers of the form 16^n * (16^n - 1) - 1 is almost a repdigit in base 16 (i.e., a repdigit with only one change).

n is in the sequence iff 4*n is in A098845. - Robert Israel, Dec 14 2015

Links

• Brady Haran and Simon Pampena, Glitch Primes and Cyclops Numbers, Numberphile video (2015)

Crossrefs

Cf. A098845, similar sequences listed in A265481.

Programs

Magma

[n: n in [1..200] | IsPrime(256^n-16^n-1)]; // Vincenzo Librandi, Dec 14 2015

Mathematica

Select[Range[1000], PrimeQ[16^# (16^# - 1) - 1] &] (* Shivam Patel, Dec 13 2015 *)

PARI

is(n)=ispseudoprime(16^n * (16^n - 1) - 1) \\ Anders Hellström, Dec 13 2015

Extensions

a(12)-a(16) computed from A098845 by Ray Chandler, Sep 25 2019