21099

Appears in sequences

• Odd 9-gonal (or enneagonal) numbers.at n=39A028991
• Expansion of g.f.: (1-2*x)/(1-3*x+2*x^3).at n=11A052948
• Group successively larger composite numbers so that the sum of the n-th group is a multiple of n. Sequence gives the sum of the terms in the n-th group.at n=38A074120
• a(n) is the least nonsquare having square residues modulo each of the first n primes.at n=12A090983
• Enneagonal numbers for which the product of the digits is also an enneagonal number.at n=25A117052
• Least m >= 0 which when added to primorial(n) yields a square.at n=8A145781
• The number of sigma-admissible subsets of {1,2,...,n} as defined by Marzuola-Miller.at n=24A158449
• Polynomial expansion of p(x)=1/(1 - 3 x + 2 x^2 + 2 x^3 - 4 x^4 + 4 x^5 - 2 x^6 - 2 x^7 + 3 x^8 - x^9 - x^17 + 3 x^18 - 2 x^19 - 2 x^20 + 4 x^21 - 4 x^22 + 2 x^23 + 2 x^24 - 3 x^25 + x^26).at n=39A164787
• Minimal sum s of n distinct squares such that s is divisible by n.at n=38A215574
• Positions of 3's in A234323.at n=58A234804
• G.f.: Product_{m>0} (1 + x^m + 2*x^(2*m) + 3*x^(3*m)).at n=33A290269
• Birooted trees: number of unlabeled trees with n nodes rooted at 2 indistinguishable roots.at n=11A303833
• a(n) is the least number k that is not a quadratic residue modulo prime(n) but is a quadratic residue modulo all previous primes.at n=12A377212
• Number of asymmetric polyominoes in {4,5} tessellation of the hyperbolic plane.at n=9A390191