21015

Appears in sequences

• a(n) = A134955(n) - A134955(n-1). Number of hyperforests spanning n unlabeled nodes without isolated vertices.at n=12A144959
• a(n) = 841*n^2 - 2*n.at n=4A158401
• Numbers k such that k-4, k-2, k+2 and k+4 are prime.at n=19A173037
• Counting integers normally (1, 2, 3, 4, 5...), write them as roman numerals (I, II, III, IV, V...), describe them (one 1, two 1s, three 1s, one 1 one 5, one 5...), and write them out as numbers (11, 21, 31, 1115, 15...).at n=24A180105
• Snub dodecahedron with faces of centered polygons.at n=7A193249
• Number of sets of nonempty words with a total of n letters over quaternary alphabet containing the fourth letter such that within each prefix of a word every letter of the alphabet is at least as frequent as the subsequent alphabet letter.at n=7A293885
• Expansion of Product_{k>=1} (1 - p(k)*x^k), where p(k) = number of partitions of k (A000041).at n=29A304785
• Sum of the prime numbers in, but not on the border of, an n X n square array whose elements are the numbers from 1..n^2, listed in increasing order by rows.at n=22A344847
• Number of compositions (ordered partitions) of n into at most 5 prime powers (including 1).at n=43A347775
• a(n) is the number of isosceles trapezoids in a triangular grid of side length n.at n=17A389363