

A182180


Semiprimes that become prime when their digits are sorted into nonincreasing order.


1



14, 34, 35, 38, 118, 119, 121, 133, 134, 142, 143, 145, 146, 166, 194, 214, 215, 218, 314, 334, 341, 346, 358, 361, 365, 377, 386, 395, 398, 413, 415, 437, 451, 473, 514, 517, 538, 583, 614, 634, 635, 671, 734, 737, 778, 779, 791, 799, 818, 835, 838, 878, 893
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OFFSET

1,1


COMMENTS

Suggested by Kevin L. Schwartz.


LINKS

Alois P. Heinz, Table of n, a(n) for n = 1..1000


EXAMPLE

a(10) = 121 = 11*11, which becomes the prime 211 when its digits are sorted into nonincreasing order.


MAPLE

h:= proc(m) local k; for k from m+1 while isprime(k) or
add(i[2], i=ifactors(k)[2])<>2 do od; k
end:
a:= proc(n) option remember; local k;
k:= h(a(n1));
do if isprime(parse(cat(sort(convert(k, base, 10), `>`)[])))
then return k else k:=h(k) fi
od
end: a(0):=0:
seq(a(n), n=1..80); # Alois P. Heinz, Apr 23 2012


CROSSREFS

Cf. A000040, A001358, A115670 Semiprimes (A001358) whose digit reversal is prime, A182150 Semiprimes that are also semiprime when their digits are sorted into nondecreasing order.
Sequence in context: A065933 A276715 A115670 * A112878 A175559 A158899
Adjacent sequences: A182177 A182178 A182179 * A182181 A182182 A182183


KEYWORD

nonn,base,easy


AUTHOR

Jonathan Vos Post, Apr 23 2012


EXTENSIONS

More terms from Alois P. Heinz, Apr 23 2012


STATUS

approved



