21931

Appears in sequences

• Deceptive nonprimes: composite numbers k that divide the repunit R_{k-1}.at n=29A000864
• Number of rational knots (or two-bridge knots) with n crossings (up to mirroring).at n=16A018240
• Strong pseudoprimes to base 10.at n=10A020236
• Strong pseudoprimes to base 100.at n=30A020326
• Numbers k such that the period of the continued fraction for sqrt(k) contains exactly 19 ones.at n=19A031787
• Gaps of 6 in sequence A038593 (upper terms).at n=6A038652
• First gap of n in sequence A038593 (lower terms).at n=12A038661
• Numbers m such that the factorizations of m..m+4 have the same number of primes (including multiplicities).at n=14A045941
• Square loops: the number of circular permutations (reversals not counted as different) of the numbers 1 to n such that the sum of any two consecutive numbers is a square.at n=13A071984
• a(n+2) = a(n+1) + a(n) - (2*n + 1) where a(0)=7, a(1)=11.at n=18A088981
• Duplicate of A018240.at n=16A090596
• a(n) = 12*n^2 + 18*n + 7.at n=42A154105
• Number of (w,x,y) with all terms in {0,...,n} and 2*max(w,x,y) >= 3*min(w,x,y).at n=28A213392
• a(n) = (1^n + (-2)^n + 4^n)/3.at n=8A245489
• Number of 6-ascent sequences of length n with no consecutive repeated letters.at n=6A264911
• Number of n-ascent sequences of length n with no consecutive repeated letters.at n=6A264916
• Numbers n such that n, n + 1, n + 2, n + 3 and n + 4 are products of exactly three primes.at n=13A268588
• Minimum BDD size of the middle bit Boolean function of multiplication of two n-bit numbers for optimum orderings of variables.at n=11A324585
• Odd composite integers m such that U(m)^2 == 1 (mod m) and V(m) == 7 (mod m), where U(m) and V(m) are the m-th generalized Lucas and Pell-Lucas numbers of parameters a=7 and b=-1, respectively.at n=33A337630
• Odd numbers k such that A064989(k) is in A340151.at n=31A340091