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A127995 Numbers n such that (20^n - 1)/19 is prime. 23
3, 11, 17, 1487, 31013, 48859, 61403 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.

LINKS

Table of n, a(n) for n=1..7.

H. Lifchitz, Mersenne and Fermat primes field

MATHEMATICA

Select[Prime[Range[100]], PrimeQ[(20^#-1)/19]&]

PROG

(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 05 2010]

(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 08 2010]

CROSSREFS

Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127996, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005.

Sequence in context: A128346 A128031 A194128 * A119141 A225144 A228470

Adjacent sequences:  A127992 A127993 A127994 * A127996 A127997 A127998

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Feb 11 2007

EXTENSIONS

One more term from Ryan Propper, Mar 29 2007

a(5)=31013 & a(6)=48859 are probable primes discovered by Paul Bourdelais, Mar 05 2010

a(7)=61403 is a probable prime discovered by Paul Bourdelais, Mar 08 2010

STATUS

approved

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Last modified November 23 22:48 EST 2014. Contains 249866 sequences.