18540

Appears in sequences

• Numbers k such that k-1, k+1 and k^2+1 are prime numbers.at n=35A070155
• a(1)=1, a(2)=2; for n >= 2, a(n+1) = a(n) + sum of prime factors of a(n).at n=37A096461
• Numbers k such that k*((2^61-1)^2) - 1 and k*((2^61-1)^2) + 1 are twin primes.at n=6A099229
• Numbers m such that m^4-1 has no divisors d with 1 < d < m-1.at n=36A129293
• Row sums of triangle A131321.at n=14A131322
• Averages of twin primes such that the sum of the lower, average and upper parts of the twin primes are averages of other twin primes.at n=10A132929
• a(n) = Sum_{k=0..n} binomial(n+k,2k)*Fibonacci(2k+1).at n=7A166482
• Number of 7-step one space at a time bishop's tours on an n X n board summed over all starting positions.at n=8A187160
• Number of 4-step S, NW and NE-moving king's tours on an n X n board summed over all starting positions.at n=27A187378
• a(n+1) is the sum of a(n) and the prime factors of a(n), counted with multiplicity. Start with a(0) = 3.at n=21A192896
• Practical numbers m with m-1 and m+1 both prime, and prime(m)-1 and prime(m)+1 both practical.at n=8A257922
• Number of (n+1) X (4+1) arrays of permutations of 0..n*5+4 with each element having directed index change 1,0 1,1 0,-1 or -1,1.at n=6A264565
• T(n,k)=Number of (n+1)X(k+1) arrays of permutations of 0..(n+1)*(k+1)-1 with each element having directed index change 1,0 1,1 0,-1 or -1,1.at n=51A264569
• Number of (7+1)X(n+1) arrays of permutations of 0..n*8+7 with each element having directed index change 1,0 1,1 0,-1 or -1,1.at n=3A264575
• Average of twin prime pairs that is a product of two averages of twin prime pairs.at n=35A307758
• Sum of all the parts in the partitions of n into 7 parts.at n=30A308926
• Number of partitions of n with ten parts in which no part occurs more than twice.at n=34A320598
• Number of compositions of n with distinct differences up to sign.at n=24A325552
• a(n) is the least positive integer k having a proper divisor d such that the base n expansions of k and d, without leading zeros, have, up to order, the same digits, or a(n) = -1 if no such k exists.at n=44A382946