A137811 Number of digits in the n-th Woodall prime.

1, 2, 3, 11, 25, 27, 37, 40, 78, 112, 119, 142, 157, 229, 251, 1603, 2339, 2874, 3731, 4768, 5690, 6920, 6930, 29725, 43058, 45468, 200815, 359799, 382007, 441847, 606279, 712818, 1129757, 5122515

Offset

1,2

Comments

Woodall primes are prime numbers of the form k*2^k-1.

Links

Table of n, a(n) for n=1..34.

Allan Cunningham and H. J. Woodall, Factorisation of Q=(2^q+-q) and (q 2^q+-1), Messenger Math., Vol. 47 (1917), pp. 1-38.

Wilfrid Keller, New Cullen Primes, Mathematics of Computation, Vol. 64, No. 212 (Ocober 1995), pp. 1733-1741.

Woodhall Primes, Definition And Status.

Formula

a(n) = A055642(A050918(n)).

Example

As the sixth Woodall prime is a 27-digit number, we have a(6)= 27

Mathematica

IntegerLength/@Select[Table[n 2^n-1, {n, 10000}], PrimeQ] (* The program generates the first 18 terms of the sequence. *) (* Harvey P. Dale, Feb 05 2023 *)

Crossrefs

Cf. A055642, A050918, A137716, A002234.

Sequence in context: A374914 A065849 A136402 * A041955 A239445 A157161

Adjacent sequences: A137808 A137809 A137810 * A137812 A137813 A137814

Keyword

nonn,base,hard,more

Author

Ant King, Feb 12 2008

Extensions

a(28)-a(34) from Amiram Eldar, Jul 19 2025

Status

approved