OFFSET
1,1
COMMENTS
Tetradic primes are primes that are palindromes and use only the digits 0, 1 and 8, so they read the same backwards and upside down. a(1) = 11, a(3) = 293 and a(21) = 11694372101 are primes.
LINKS
Eric Weisstein's World of Mathematics, Tetradic Number.
FORMULA
EXAMPLE
a(21) = 11 + 101 + 181 + 18181 + 1008001 + 1180811 + 1880881 + 1881881 + 100111001 + 100888001 + 108101801 + 110111011 + 111010111 + 111181111 + 118818811 + 180101081 + 181111181 + 181888181 + 188010881 + 188888881 + 10008180001 = 11694372101.
CROSSREFS
KEYWORD
base,easy,nonn,less
AUTHOR
Jonathan Vos Post, Jun 16 2006
EXTENSIONS
Corrected by Jens Kruse Andersen, Apr 27 2010
STATUS
approved