OFFSET
1,2
FORMULA
For each term a(n) in this sequence, A080153(n) = prime(a(n)).
EXAMPLE
E.g. the first three terms are 1, 2 and 5 because the concatenation of the first, 2nd and 11th primes is 2311 and this is prime. Also, the 5th prime is the first one after 3 for which this concatenation is prime.
MAPLE
with(numtheory): pout := [2, 3]: nout := [1, 2]: for n from 3 to 600 do: p := ithprime(n): d := parse(cat(pout[nops(pout)-1], pout[nops(pout)], p)): if (isprime(d)) then pout := [op(pout), p]: nout := [op(nout), n]: fi: od: nout;
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 31 2003
EXTENSIONS
Edited by Charles R Greathouse IV, Apr 30 2010
STATUS
approved