login
A111479
a(n) = least positive number such that (2 Concat Concat_{k=1}^n Repeat(A045572(n), a(n))) is a prime. A045572 = odd numbers not divisible by 5.
1
2, 1, 4, 11, 3, 617, 96, 1213, 1965
OFFSET
1,1
COMMENTS
Concat is the operator that concatenates two numbers as decimal strings and Repeat returns the number obtained by concatenating the first argument to itself the second argument number of times.
EXAMPLE
21 is not a prime, but 211 is, so a(1)=2.
211,2113,21137777 are all primes. 21137777 is a prime obtained as 2 followed by two 1's, one 3 and four 7's, so a(2) = 4.
KEYWORD
base,more,nonn,less
AUTHOR
Amarnath Murthy, Aug 05 2005
EXTENSIONS
Edited by Franklin T. Adams-Watters, Aug 29 2006.
Corrected and extended by Max Alekseyev, May 21 2009
STATUS
approved