OFFSET
4,1
EXAMPLE
a(7) = 1909081 is the last among 7-digit emirp pairs (1909081, 1809091) which rotated through 180 degrees forms another emirp pair (1806061, 1606081).
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Lekraj Beedassy, May 03 2010
EXTENSIONS
More terms from Giovanni Resta, Aug 14 2019
STATUS
approved