145289domain: NPropertiesPrimalityPrimeyesAppears in sequencesNumbers n such that 2^n - 21 is prime.at n=33A057202Numbers k such that 2^k - 21 is prime.at n=29A096820Number of horizontal steps in the peaks of all bargraphs having semiperimeter n (n>=2).at n=11A273720Primes formed by concatenating n and 2n-1.at n=40A309851Prime numbersat n=13445