218107

Properties

Appears in sequences

• a(1) = 1; for n>1, a(n) = the largest prime divisor of the number C(n) formed from the concatenation of n, n-1, n-2, n-3, ... down to 1.at n=5A075021
• a(1) = 1, a(n) = the largest prime divisor of A138793(n).at n=5A138963
• Primes of the form p^2 + 18, where p is prime.at n=38A201688
• Numbers k such that Sum_{j=1..k-1} (4j)!/16^j is an integer.at n=9A216044
• Prime numbersat n=19452