21937

Properties

Appears in sequences

• Lesser of two consecutive primes such that p + n*q is a perfect square, p < q.at n=40A064543
• Primes p such that q = 4p^2 + 1 and r = 4q^2 + 1 are also prime.at n=31A122424
• Number of tilings of a 3 X n rectangle with n trominoes.at n=11A134438
• Primes p0 such that p0+p1+p2-+2 are primes; p0,p1,p2 are three consecutive primes.at n=22A158351
• Number of n X n binary arrays without the pattern 0 0 0 antidiagonally or horizontally.at n=3A188867
• Number of n X 4 binary arrays without the pattern 0 0 0 antidiagonally or horizontally.at n=3A188869
• T(n,k)=Number of nXk binary arrays without the pattern 0 0 0 antidiagonally or horizontally.at n=24A188874
• Number of 4Xn binary arrays without the pattern 0 0 0 antidiagonally or horizontally.at n=3A188876
• Primes of form n^2 + 6561.at n=13A256837
• Smallest integer k_1 such that there exist n positive integers k_1 > k_2 > ... > k_n having the property that k_j * k_n > k_(j+1)^2 for j=1..n-1.at n=13A259762
• Triangle read by rows, giving the arithmetic progressions of prime-indexed primes in A278735.at n=11A279021
• Number of sets of exactly n positive integers <= n+6 having a square element sum.at n=26A281969
• Prime time primes (of the form HMMSS with primes H < 24 and MM, SS < 60) such that the corresponding number of seconds after midnight is also prime.at n=14A295000
• Number of cyclic binary sequences of length n containing no abelian 4th powers.at n=37A305594
• Expansion of Sum_{k>=1} x^k/(1 - x^k - 2*x^(2*k)).at n=15A309729
• a(n) = Sum_{k=1..n} 2^(k/gcd(n,k) - 1).at n=15A338647
• Number of alternating strict compositions of n. Number of alternating (up/down or down/up) permutations of strict integer partitions of n.at n=34A349054
• Prime numbersat n=2459