21606

Appears in sequences

• Aliquot sequence starting at 138.at n=16A008888
• Aliquot sequence starting at 150.at n=15A008889
• Aliquot sequence starting at 168.at n=13A008890
• Aliquot sequence starting at 570.at n=11A074907
• G.f.: A(x) = Sum_{n>=0} (1 + x)^(n^2) / 2^(n+1).at n=4A173217
• Products of four distinct primes between sphenic numbers (products of 3 distinct primes).at n=12A351382
• Expansion of e.g.f. 1 / ( 1 - Sum_{k>=0} x^(3*k+5) / (3*k+5)! ).at n=16A365916
• a(n) = Sum_{k=0..n} binomial(k+2,2) * binomial(2*k,2*n-2*k).at n=8A382230