OFFSET
1,2
COMMENTS
Conjecture: 2 and 5 are the only two nonmembers.
EXAMPLE
a(3)=49 => 349 is a prime but not necessarily 1349, which by the way it
is not.
MATHEMATICA
p = Prime[ Range[ 500]]; np = Drop[ Complement[ Range[ 500], p], 1]; a[1] = 1; a[n_] := a[n] = Block[{k = 1, q = IntegerDigits[a[n - 1]]}, If[ EvenQ[n], While[ !PrimeQ[ FromDigits[ Join[q, IntegerDigits[ p[[k]] ]]]], k++ ]; q = p[[k]]; p = Delete[p, k]; q, While[ !PrimeQ[ FromDigits[ Join[q, IntegerDigits[ np[[k]] ]]]], k++ ]; q = np[[k]]; np = Delete[np, k]; q]]; Table[ a[n], {n, 60}]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Robert G. Wilson v, Apr 23 2004
STATUS
approved