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A345664
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Primes whose digit reversal is the product of two (not necessarily distinct) emirps.
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0
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1187, 1291, 1621, 1931, 3119, 3637, 3833, 3989, 7069, 7129, 7411, 9049, 9181, 9461, 9631, 10103, 10589, 10597, 10691, 12517, 12653, 12703, 13487, 13999, 14771, 14969, 15319, 15359, 16183, 16253, 16411, 16421, 16477, 16823, 16901, 17027, 17881, 18061, 18121, 19079, 19121, 19427, 19507, 19739
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..44.
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EXAMPLE
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a(3) = 1621 is a term because 1621 is prime and its digit reversal is 1261 = 13*97 where 13 and 97 are emirps.
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MAPLE
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digrev:= proc(n) local L, i;
L:= convert(n, base, 10);
add(L[-i]*10^(i-1), i=1..nops(L))
end proc:
isemirp:= proc(p) local r;
if not isprime(p) then return false fi;
r:= digrev(p);
r <> p and isprime(r)
end proc:
E:= select(isemirp, [seq(seq(seq(i*10^d+j, j=1..10^d-1, 2), i=[1, 3, 7, 9]), d=1..3)]):
R:= NULL:
for i from 1 to nops(E) do
for j from 1 to i do
v:= E[i]*E[j];
if v > 10^5 then break fi;
v:= digrev(v);
if isprime(v) then R:= R, v fi
od od:
sort([R]);
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CROSSREFS
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Cf. A006567.
Sequence in context: A345540 A345792 A237698 * A052236 A342066 A153378
Adjacent sequences: A345661 A345662 A345663 * A345665 A345666 A345667
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KEYWORD
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nonn,base
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AUTHOR
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J. M. Bergot and Robert Israel, Jun 21 2021
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STATUS
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approved
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