cp's OEIS Frontend

A224402 Composite numbers that become prime when their digits are put in nonincreasing order.

%I A224402 #11 Apr 23 2013 11:14:58
%S A224402 14,16,34,35,38,112,118,119,121,124,125,128,133,134,136,142,143,145,
%T A224402 146,152,154,164,166,175,176,182,188,194,214,215,218,314,316,334,341,
%U A224402 343,344,346,356,358,361,364,365,368,374,377,385,386,388,395,398,412,413
%N A224402 Composite numbers that become prime when their digits are put in nonincreasing order.
%C A224402 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.
%H A224402 Christian N. K. Anderson, <a href="/A224402/b224402.txt">Table of n, a(n) for n = 1..10000</a>
%e A224402 194=2*97, but 941 is prime.
%t A224402 Select[Range[500], ! PrimeQ[#] && PrimeQ[FromDigits[Reverse[Sort[IntegerDigits[#]]]]] &] (* _T. D. Noe_, Apr 05 2013 *)
%o A224402 (R) j=1; y=c(); library(gmp)
%o A224402 while(length(y)<1000) {
%o A224402 if(isprime((j=j+1))==0) {
%o A224402 x=sort(as.numeric(strsplit(as.character(j),spl="")[[1]]),decr=T)
%o A224402 if(isprime(paste(x,collapse=""))>0) y=c(y,j)
%o A224402 }
%o A224402 }
%Y A224402 Subset of A007935.
%Y A224402 Cf. A068653, A076055, A224400.
%K A224402 nonn,base
%O A224402 1,1
%A A224402 _Christian N. K. Anderson_ and _Kevin L. Schwartz_, Apr 05 2013