A224400 Composite numbers that become prime when their digits are put in nondecreasing order.
20, 30, 32, 50, 70, 74, 76, 91, 92, 95, 98, 110, 130, 170, 172, 175, 176, 190, 194, 200, 203, 209, 217, 230, 232, 272, 275, 290, 292, 296, 300, 301, 302, 310, 319, 320, 322, 323, 329, 332, 370, 371, 374, 376, 391, 392, 394, 395, 398, 407, 437, 470, 473, 475
Offset: 1
Examples
217 = 7*31, but 127 is prime. 302 = 2*151, but 23 is prime.
Links
- Christian N. K. Anderson, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
Select[Range[500], ! PrimeQ[#] && PrimeQ[FromDigits[Sort[IntegerDigits[#]]]] &] (* T. D. Noe, Apr 05 2013 *)
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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]])) if(isprime(paste(x[x>0],collapse=""))>0) y=c(y,j) #drop leading zeros } }
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