OFFSET
1,1
COMMENTS
a(7) > 4294967296.
Terms in A020449 are not terms of this sequence. - Chai Wah Wu, Jun 18 2020
a(8) > 10^13, if it exists. - Giovanni Resta, Jun 21 2020
EXAMPLE
a(3)=13 because 13 -> 19 -> 181 are primes and 1641 is composite.
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Carlos Rivera, Jun 10 2020
EXTENSIONS
a(7) from Giovanni Resta, Jun 20 2020
STATUS
approved