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Primes p such that the sum of p and its reversal is a semiprime.
2

%I #10 Dec 01 2023 15:55:57

%S 2,3,5,7,11,23,29,41,43,47,61,67,83,89,101,131,151,181,191,211,223,

%T 227,233,251,293,313,353,373,383,401,409,419,421,431,433,449,457,487,

%U 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

%N Primes p such that the sum of p and its reversal is a semiprime.

%C Terms > 11 with an even number of digits have an even first digit.

%H Robert Israel, <a href="/A367793/b367793.txt">Table of n, a(n) for n = 1..10000</a>

%e a(6) = 23 is a term because 23 is a prime and 23 + 32 = 55 = 5 * 11 is a semiprime.

%p digrev:= proc(n) local L,i;

%p L:= convert(n,base,10);

%p add(L[-i]*10^(i-1),i=1..nops(L))

%p end proc:

%p select(p -> isprime(p) and numtheory:-bigomega(p+digrev(p))=2, [2,seq(i,i=3..10000,2)]);

%t Select[Prime[Range[10^4]], 2 == PrimeOmega[# + FromDigits[Reverse[IntegerDigits[#]]]] &]]

%Y Cf. A001358, A056964, A061783.

%K nonn,base

%O 1,1

%A _Zak Seidov_ and _Robert Israel_, Nov 30 2023