A367793 Primes p such that the sum of p and its reversal is a semiprime.

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

Offset

1,1

Comments

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

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

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

Maple

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)]);

Mathematica

Select[Prime[Range[10^3]], 2 == PrimeOmega[# + FromDigits[Reverse[IntegerDigits[#]]]] &]

Crossrefs

Cf. A001358, A056964, A061783.

Sequence in context: A078403 A129945 A046704 * A386004 A089392 A089695

Adjacent sequences: A367790 A367791 A367792 * A367794 A367795 A367796

Keyword

nonn,base

Author

Zak Seidov and Robert Israel, Nov 30 2023

Status

approved