280800

Appears in sequences

• Theta series of direct sum of 5 copies of hexagonal lattice.at n=10A008656
• Number of double-free subsets of {1, 2, ..., n}.at n=22A050291
• Sum of divisors of those numbers n such that n and n+1 have the same sum of divisors.at n=31A053215
• Numbers k such that core(k) = b(k,1)*b(k,0) where b(k,1) is the number of 1's in binary representation of k, b(k,0) the number of 0's and core(k) the squarefree part of k.at n=18A071639
• Sigma(A033631(n)) {sigma is the sum of divisors function A000203}.at n=31A115619
• Triangle read by rows: coefficient of x^n in the Taylor expansion of x/(1 - m*x - x^4) in row n, column m=1..n+2.at n=50A117742
• If X_1,...,X_n is a partition of a 2n-set X into 2-blocks then a(n) is equal to the number of 4-subsets of X containing none of X_i, (i=1,...,n).at n=23A130810
• Amicable triples. Sequence gives sigma values: A125490(n) + A125491(n) + A125492(n).at n=19A137231
• Numbers with exactly four distinct exponents in their prime factorization, or four distinct parts in their prime signature.at n=23A323025
• Terms of A301517 that are not exponentially odd numbers (A268335).at n=26A335989
• a(n) is the smallest number k for which k and the arithmetic derivative k' (A003415) have exactly n triangular divisors (A000217).at n=13A357842