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A084632
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Semiprimes such that when they are concatenated with their 10's complement, which also must be a semiprime, the result is a prime.
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1
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49, 91, 169, 237, 319, 321, 329, 377, 411, 417, 473, 529, 553, 583, 597, 629, 697, 713, 763, 779, 791, 817, 913, 923, 949, 1203, 1257, 1273, 1339, 1347, 1379, 1389, 1497, 1501, 1509, 1529, 1589, 1633, 1739, 1803, 1841, 1967, 1969, 2019, 2103, 2173, 2219
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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LINKS
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Harvey P. Dale, Table of n, a(n) for n = 1..1000
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EXAMPLE
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a(3)=169 because 169 is a semiprime and 1000-169 = 831 is a semiprime, while 169831 is a prime.
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MATHEMATICA
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sctQ[n_]:=Module[{tc=10^IntegerLength[n]-n, j}, j=n*10^IntegerLength[ tc]+ tc; PrimeOmega[tc]==PrimeOmega[n]==2&&PrimeQ[j]]; Select[Range[ 2300], sctQ] (* Harvey P. Dale, Jan 02 2019 *)
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CROSSREFS
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Cf. A001358.
Sequence in context: A320633 A108164 A020158 * A020176 A146064 A224905
Adjacent sequences: A084629 A084630 A084631 * A084633 A084634 A084635
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KEYWORD
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nonn,base
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AUTHOR
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Jason Earls, Jun 28 2003
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STATUS
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approved
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