21361

Appears in sequences

• Pseudoprimes to base 5.at n=31A005936
• Pseudoprimes to base 60.at n=37A020188
• Pseudoprimes to base 63.at n=40A020191
• Strong pseudoprimes to base 12.at n=15A020238
• Strong pseudoprimes to base 60.at n=14A020286
• Strong pseudoprimes to base 63.at n=19A020289
• Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 11.at n=24A031599
• Values of c in a^2 + b^2 = c^2 where b - a = 31 and gcd(a,b)=1.at n=7A116509
• Number of permutations of length n which avoid the patterns 321, 2143, 3124; or avoid the patterns 132, 2314, 4312, etc.at n=40A116731
• Terms of A122782 which are not Carmichael numbers A002997.at n=40A153515
• Positive numbers y such that y^2 is of the form x^2 + (x+31)^2 with integer x.at n=12A157646
• 28-gonal numbers: a(n) = n*(13*n - 12).at n=41A161935
• a(n) = 1 + 4*n*(1 + 2*n^2)/3.at n=20A171272
• Quartan semiprimes: semiprimes of the form x^4 + y^4, x>0, y>0.at n=17A182277
• Wiener index of a benzenoid consisting of a double-step spiral chain of n hexagons (n>=2, s=21; see the Gutman et al. reference).at n=14A193397
• Euler pseudoprimes to base 5: composite integers such that abs(5^((n - 1)/2)) == 1 mod n.at n=17A262052
• a(n) is the smallest composite (pseudoprime) p such that Bell(n+p) == Bell(n)+Bell(n+1) (mod p).at n=0A286635
• a(n) = (2*prime(n)^2 + 1)/3.at n=38A286679
• Number of nX5 0..1 arrays with every element equal to 1, 2, 4, 5 or 6 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero.at n=5A303407
• T(n,k)=Number of nXk 0..1 arrays with every element equal to 1, 2, 4, 5 or 6 horizontally, diagonally or antidiagonally adjacent elements, with upper left element zero.at n=50A303410