

A054416


Numbers n such that 9090...9091 (with n1 copies of 90 and one copy of 91) is prime.


3




OFFSET

1,1


REFERENCES

J. A. H. Hunter and J. S. Madachy, Mathematical Diversions, New York: Dover Publications, Inc., 1974, pp. 45. Originally published by Van Nostrand, 1963.


LINKS

Table of n, a(n) for n=1..10.
D. Broadhurst, Proof that 1505 term is prime


FORMULA

10*(10^(2n)1)/11 + 1 is prime.


EXAMPLE

The first 3 numbers are 9091, 909091, 909090909090909091


MATHEMATICA

Do[ If[ PrimeQ[ 10*(10^(2n)  1)/11 + 1], Print[ n ] ], {n, 0, 1505} ]
Position[Table[FromDigits[PadLeft[{9, 1}, 2n, {9, 0}]], {n, 1510}], _?PrimeQ]// Flatten (* Harvey P. Dale, Nov 02 2017 *)


CROSSREFS

Equals (A0015621)/2.
Sequence in context: A061933 A251239 A124881 * A291868 A092638 A206777
Adjacent sequences: A054413 A054414 A054415 * A054417 A054418 A054419


KEYWORD

nonn


AUTHOR

Antreas P. Hatzipolakis (xpolakis(AT)otenet.gr), May 22 2000


EXTENSIONS

More terms from Michael Kleber and Harvey Dubner (harvey(AT)dubner.com), May 22, 2000
Ignacio Larrosa CaĆ±estro reports that the 1068 term has now been established to be a prime using Titanix 1.01, Oct 23 2000


STATUS

approved



