OFFSET
1,1
COMMENTS
Because any number ending in zero is composite, the sequence experiences gaps of at least order O(a(n))-1 between changes in the most significant digit.
LINKS
Christian N. K. Anderson, Table of n, a(n) for n = 1..10000
EXAMPLE
194=2*97, but 941 is prime.
MATHEMATICA
Select[Range[500], ! PrimeQ[#] && PrimeQ[FromDigits[Reverse[Sort[IntegerDigits[#]]]]] &] (* T. D. Noe, Apr 05 2013 *)
PROG
(R) j=1; y=c(); library(gmp)
while(length(y)<1000) {
if(isprime((j=j+1))==0) {
x=sort(as.numeric(strsplit(as.character(j), spl="")[[1]]), decr=T)
if(isprime(paste(x, collapse=""))>0) y=c(y, j)
}
}
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Christian N. K. Anderson and Kevin L. Schwartz, Apr 05 2013
STATUS
approved