21119

Appears in sequences

• Numbers k > 1 such that k mod ord2(k) is even, where ord2(k) is the order of 2 mod k.at n=31A036260
• Numbers n such that phi(2n-1) = sigma(n).at n=42A067230
• Number of set partitions of {1, ..., n} that avoid 4-crossings.at n=9A108305
• Number of n X n binary arrays symmetric under 180 degree rotation with all ones connected only in a 1000-1100-0111-0001 pattern in any orientation.at n=10A147282
• Number of (n+1) X 2 0..1 arrays with the number of rightwards and downwards edge increases in each 2 X 2 subblock equal to the number in all its horizontal and vertical neighbors.at n=17A206260
• Numbers with 3 or more prime factors (with multiplicity) such that every concatenation of their prime factors is prime.at n=24A217264
• a(n) = floor(1/(zeta(5) - Sum_{h=1..n} 1/h^5)).at n=7A248234
• Decimal representation of the x-axis, from the left edge to the origin, of the n-th stage of growth of the two-dimensional cellular automaton defined by "Rule 369", based on the 5-celled von Neumann neighborhood.at n=28A281516
• Numbers k such that k!4 + 2^4 is prime, where k!4 = k!!!! is the quadruple factorial number (A007662).at n=33A291344
• Numbers of the form HMMSS with primes H < 24 and MM, SS < 60, for which the number of seconds after midnight, 3600*H+60*MM+SS, is also prime.at n=23A295011
• Regular triangle read by rows where T(n, k) is the number of set partitions of {1, ..., n} with no block containing k cyclically successive vertices, n >= 1, 2 <= k <= n + 1.at n=41A323955