A103100 - OEIS

A103100

Numbers n such that 9*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

0, 3, 6, 18, 30, 88, 93, 154, 177, 228, 573, 897, 981, 1416, 1450, 3366, 4932, 5194, 13479, 18609, 23346, 51424, 74676, 80571

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OFFSET

1,2

COMMENTS

Also numbers n such that (86*10^n-41)/9 is prime.

a(25) > 10^5. - Robert Price, Nov 10 2015

LINKS

FORMULA

a(n) = A101009(n-1) + 1, for n>1.

EXAMPLE

For n=0, (86*10^n - 41)/9 = 5 which is prime.

MATHEMATICA

Do[ If[ PrimeQ[(86*10^n - 41)/9], Print[n]], {n, 0, 10000}]

PROG

(PARI) for(n=0, 1e3, if(ispseudoprime((86*10^n-41)/9), print1(n, ", "))) \\ Altug Alkan, Nov 10 2015

CROSSREFS

KEYWORD

more,nonn

AUTHOR

EXTENSIONS

a(19)-a(21) from Kamada data by Robert Price, Dec 14 2010

Inserted a(1)=0 and added a(22)-a(24) by Robert Price, Nov 10 2015

STATUS

approved