21876

Appears in sequences

• a(n) = p(1)p(n) + p(2)p(n-1) + ... + p(k)p(n+1-k), where k = [ (n+1)/2 ], p = A000040 = the primes.at n=28A024697
• Numbers k such that k^4 == 1 (mod 5^5).at n=28A056102
• a(n) is the position of a(n-1) in the decimal expansion of Pi, starting with a(1)=13.at n=16A119744
• a(n) = 625*n + 1.at n=34A158383
• Divisors of 196884.at n=18A199014
• a(n) = 7*5^n+1.at n=5A199310
• L.g.f.: Sum_{n>=1} x^n/n * Product_{d|n} (1 + d*x^n)^d.at n=24A205483
• Sum of numbers in the n-th antidiagonal of the reciprocity array of 1.at n=44A259577
• Numbers that are the sum of seven fourth powers in seven or more ways.at n=10A345573
• Numbers that are the sum of seven fourth powers in eight or more ways.at n=6A345574
• Numbers that are the sum of seven fourth powers in exactly eight ways.at n=3A345830