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A224402
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Composite numbers that become prime when their digits are put in nonincreasing order.
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2
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14, 16, 34, 35, 38, 112, 118, 119, 121, 124, 125, 128, 133, 134, 136, 142, 143, 145, 146, 152, 154, 164, 166, 175, 176, 182, 188, 194, 214, 215, 218, 314, 316, 334, 341, 343, 344, 346, 356, 358, 361, 364, 365, 368, 374, 377, 385, 386, 388, 395, 398, 412, 413
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OFFSET
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1,1
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COMMENTS
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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.
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LINKS
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Christian N. K. Anderson, Table of n, a(n) for n = 1..10000
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EXAMPLE
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194=2*97, but 941 is prime.
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MATHEMATICA
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Select[Range[500], ! PrimeQ[#] && PrimeQ[FromDigits[Reverse[Sort[IntegerDigits[#]]]]] &] (* T. D. Noe, Apr 05 2013 *)
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PROG
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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]]), decr=T)
if(isprime(paste(x, collapse=""))>0) y=c(y, j)
}
}
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CROSSREFS
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Subset of A007935.
Cf. A068653, A076055, A224400.
Sequence in context: A228207 A175887 A305885 * A067844 A015877 A192290
Adjacent sequences: A224399 A224400 A224401 * A224403 A224404 A224405
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KEYWORD
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nonn,base
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AUTHOR
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Christian N. K. Anderson and Kevin L. Schwartz, Apr 05 2013
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STATUS
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approved
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