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A367793
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Primes p such that the sum of p and its reversal is a semiprime.
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2
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2, 3, 5, 7, 11, 23, 29, 41, 43, 47, 61, 67, 83, 89, 101, 131, 151, 181, 191, 211, 223, 227, 233, 251, 293, 313, 353, 373, 383, 401, 409, 419, 421, 431, 433, 449, 457, 487, 491, 571, 599, 601, 607, 617, 619, 631, 643, 647, 727, 757, 787, 797, 809, 821, 827, 829, 853, 859, 877, 883, 919, 929, 2011
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OFFSET
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1,1
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COMMENTS
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Terms > 11 with an even number of digits have an even first digit.
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LINKS
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EXAMPLE
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a(6) = 23 is a term because 23 is a prime and 23 + 32 = 55 = 5 * 11 is a semiprime.
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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:
select(p -> isprime(p) and numtheory:-bigomega(p+digrev(p))=2, [2, seq(i, i=3..10000, 2)]);
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MATHEMATICA
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Select[Prime[Range[10^4]], 2 == PrimeOmega[# + FromDigits[Reverse[IntegerDigits[#]]]] &]]
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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