21281

Appears in sequences

• a(n) = a(n-1) + a(n-2) + 1, with a(0) = 1 and a(1) = 6.at n=18A022320
• Number of 5-element families of an n-element set such that every 4 members of the family have a nonempty intersection.at n=5A051367
• a(n) = n*(n^2+3*n-1)/3.at n=39A084990
• Semiprimes that are the sum of the first n semiprimes for some n.at n=29A092190
• a(n) = 29 + 73*n + 37*n^2.at n=23A145980
• Positive integers of the form (10*m^2+1)/11.at n=27A179338
• T(n,k)=Number of length n+3 0..k arrays with some pair in every consecutive four terms totalling exactly k.at n=37A245950
• Number of length 2+3 0..n arrays with some pair in every consecutive four terms totalling exactly n.at n=7A245952
• Fundamental discriminants d uniquely characterizing all complex biquadratic fields Q(sqrt(-3),sqrt(d)) which have 3-class group of type (3,3) and second 3-class group isomorphic to SmallGroup(729,34).at n=8A250241
• Partial sums of A256970.at n=36A256971
• Numbers k such that (74*10^k + 313)/9 is prime.at n=18A294942
• Solution of the complementary equation a(n) = a(n-1) + a(n-2) + b(n) - n, where a(0) = 1, a(1) = 2, b(0) = 3, b(1) = 4, b(2) = 5, and (a(n)) and (b(n)) are increasing complementary sequences.at n=18A296557