21593

Appears in sequences

• Quasi-Carmichael numbers to base 9: squarefree composites n such that (n,2*3*5*7) = 1 and prime p|n ==> p-9|n-9.at n=6A029554
• n*10^4-1, n*10^4-3, n*10^4-7 and n*10^4-9 are all prime.at n=5A064978
• Numbers k such that 8*10^k + 6*R_k + 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.at n=14A103088
• Number of ways to partition a 3*n X 2 grid into 6 connected equal-area regions.at n=10A167240
• -7-Knödel numbers.at n=22A225511
• Composite squarefree numbers n such that p(i)-7 divides n+7, where p(i) are the prime factors of n.at n=16A225707
• Number of hairpin compositions of n.at n=16A338740
• Array read by antidiagonals: T(n,k) is the number of n X n nonnegative integer matrices with sum of elements equal to k, up to rotations and reflections.at n=70A343875