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A137716
Number of digits in the decimal expansion of the n-th Cullen prime.
1
1, 45, 1423, 1749, 1994, 5573, 9726, 9779, 17964, 27347, 79002, 108761, 145072, 407850, 1905090, 2010852
OFFSET
1,2
COMMENTS
Cullen primes are prime numbers of the form k*2^k+1. This sequence is complete for all values of n up to 3500000.
LINKS
Ray Ballinger and Mark Rodenkirch, Cullen Primes: Definition and Status.
James Cullen, Question 15897, The Educational Times, Dec. 1905, p. 534.
Allan Cunningham and H. J. Woodall, Factorisation of Q=(2^q ± q) and (q*2^q ± 1), The Messenger of Mathematics, Vol. 47 (1917-18), pp. 1-38.
Wilfrid Keller, New Cullen Primes, Mathematics of Computation, Vol. 64, No. 212 (Ocober 1995), pp. 1733-1741.
FORMULA
a(n) = A055642(A050920(n)). [Corrected by Georg Fischer, Nov 18 2023]
EXAMPLE
As the sixth Cullen prime, 18496*2^18496 + 1 = 1.311...*10^5572, is a 5573-digit number, we have a(6) = 5573.
CROSSREFS
KEYWORD
hard,nonn,base,more
AUTHOR
Ant King, Feb 09 2008
EXTENSIONS
a(15)-a(16) from Amiram Eldar, Oct 27 2024
STATUS
approved