27471

Appears in sequences

• Number of n X n binary arrays symmetric under 180 degree rotation with all ones connected only in a 10101-11111 pattern in any orientation.at n=11A147427
• Exponents k for which reversal(2^k-1) is prime.at n=12A309607
• Numbers k such that 2^k + 2*k - 3 is prime.at n=31A392535
• a(n) = 1 + Sum_{i=1..n} (p_i - 2)*(p_i#/p_i), where p_i stands for the i-th prime, and p_i# = A002110(i), the i-th primorial number.at n=6A392860