20191

Appears in sequences

• Strong pseudoprimes to base 75.at n=26A020301
• Strong pseudoprimes to base 83.at n=14A020309
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 33 ones.at n=1A031801
• a(n) = (2*n+1)*(11*n+1).at n=30A033575
• Numbers k such that the digits of k^2 are exactly the same (albeit in different order) as the digits of (k+1)^2.at n=8A072841
• Sum of the n-th row of A077339.at n=19A081929
• Numerators of the continued fraction convergents of the decimal concatenation of the lower bound of twin primes.at n=18A128844
• Numbers k such that 2^(2k-1) == 2 (mod 2k) and such that 2^(k-1) != 1 (mod k).at n=34A176033
• Number of nX4 0..4 arrays with each element x equal to the number its horizontal and vertical neighbors equal to 4,3,1,0,2 for x=0,1,2,3,4.at n=5A196900
• Number of nX6 0..4 arrays with each element x equal to the number its horizontal and vertical neighbors equal to 4,3,1,0,2 for x=0,1,2,3,4.at n=3A196902
• T(n,k)=Number of nXk 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 4,3,1,0,2 for x=0,1,2,3,4.at n=39A196904
• T(n,k)=Number of nXk 0..4 arrays with each element x equal to the number of its horizontal and vertical neighbors equal to 4,3,1,0,2 for x=0,1,2,3,4.at n=41A196904
• G.f.: Sum_{n>=0} (2 + x^n)^n * x^n / (1-x)^(n+1).at n=9A244615
• Composite numbers n such that 2^lpf(n) == 2 (mod n), where lpf(n) = A020639(n).at n=24A276733
• Records in A171797 starting from a(1).at n=39A305396