21780

Appears in sequences

• Number of paraffins.at n=43A005997
• Numbers k such that k and 4*k are anagrams.at n=14A023088
• Theta series of A*_10 lattice.at n=34A023922
• a(n) = 5*(n+1)*binomial(n+2, 5)/2.at n=7A027778
• a(n) = 4*(n+1)*binomial(n+2,8).at n=4A027781
• Numbers k such that sigma(phi(k)) = phi(sigma(k)).at n=12A033632
• a(n) = n^2 * phi(n).at n=32A053191
• Numbers k such that phi(2*sigma(k)) = 2*sigma(phi(k)).at n=14A067709
• Numbers k such that sigma(phi(k)) divides phi(sigma(k)).at n=22A073858
• Numbers n such that A001414(n) = sum of composites from the smallest prime factor of n to the largest prime factor of n.at n=9A074053
• Numbers k such that 6*k+1, 6*k+7, 6*k+13, 6*k+19 are consecutive primes.at n=23A090839
• Numbers k such that sigma(phi(k)) == phi(sigma(k)) (mod k), that is, A033632(k)/k is an integer.at n=14A092584
• Number of partitions of 2*n with no part divisible by 3 and all odd parts occurring with even multiplicities.at n=31A098151
• a(n) = n^2*(2*n+1).at n=22A099721
• Numbers that have exactly seven prime factors counted with multiplicity (A046308) whose digit reversal is different and also has 7 prime factors (with multiplicity).at n=3A109027
• Expansion of g.f.: -x*(1 - 2*x + 6*x^2 - 2*x^3 + x^4)/((1-x)^3*(1+x)^4).at n=43A122576
• a(n) = n*floor(n/2)^2.at n=45A122656
• Exponential aspiring numbers.at n=37A127658
• Exponential abundant numbers: integers k for which A126164(k) > k, or equivalently for which A051377(k) > 2k.at n=22A129575
• Minimal m > 0 such that Fibonacci(m) == 0 (mod n^3).at n=32A132633