21200

Appears in sequences

• n written in fractional base 3/2.at n=18A024629
• In the list of divisors of n (in base 3), each digit 0-2 appears equally often.at n=13A045811
• Autobiographical numbers (or curious numbers): list of numbers m = x_0 x_1 x_2 ... x_{b-1} (written in base b) such that x_i is the number of "digits" in m that are equal to i, for all i=0,...,b-1.at n=2A046043
• Numbers k such that the number of steps to reach 1 in '3x+1' problem equals tau(k), the number of divisors of k.at n=30A070980
• a(n) = n*(n - 1)*(2*n^2 + n + 2)/6.at n=16A071246
• Binary numbers with 2 replacing 1 in odd positions.at n=28A095914
• a(n) = prime(n)^2 - prime(n^2). Commutator of (primes, squares) at n.at n=44A123914
• Autobiographical numbers: the first digit specifies how many 0's in the number, the next digit specifies how many 1's, etc. This version is not limited to 10 digits.at n=2A138480
• a(n) = A000010(n) * A002088(n).at n=40A143231
• Number of walks within N^3 (the first octant of Z^3) starting at (0,0,0) and consisting of n steps taken from {(-1, -1, 0), (-1, 0, 1), (0, -1, 1), (0, 1, -1), (1, 0, 1)}.at n=9A148941
• Number of nondecreasing integer sequences of length 8 with sum zero and sum of absolute values 2n.at n=19A158142
• Triangle T : T(n,k)= binomial(n,k)*A000957(n+1-k).at n=56A171616
• Łukasiewicz words (without the last zero) for rooted plane trees where non-leaf branching can occur only at the leftmost branch of any level, but nowhere else.at n=24A209644
• The Wiener index of a link of n fullerenes C_{20} (see the Ghorbani and Hosseinzadeh reference).at n=3A216114
• 4*(n + 7)^3 - 27*(n + 7)^2 = (4*n +1)*(n+7)^2.at n=13A245033
• E.g.f. satisfies: A(x) = exp( x * Integral A(x) dx ).at n=4A274738
• Number of permutations p of [n] such that 0p has a nonincreasing down-jump sequence.at n=8A288912
• Minimum value of the cyclic autocorrelation of first n primes.at n=21A299053
• Non-palindromic numbers n such that n * reverse(n) is a square and n and reverse(n) do not have the same number of digits.at n=33A322835
• Autobiographical numbers: the first digit of the term counts how many 0's the term in total has, the second how many 1's etc. up to the last digit but no more than b-1, where b is the base of the sequence. This sequence is in base b=10.at n=2A358538