>>639

a[n] = a[n-1] + a[n-2]/{(2n-1)(2n-3)},
a[n] 〜 (1/e)(8n-5)/(8n-3)　→　1/e,

b[n] = (2n-1)b[n-1] + b[n-2],
b[n]/(2n-1)!! 〜 e (8n-5)/(8n-3)　→　ｅ,

c[n] = (2n-1)c[n-1] + c[n-2],
c[n]/(2n-1)!! 〜 (1/e)(8n-5)/(8n-3)　→　1/e,