OFFSET
1,1
COMMENTS
a(n) = A046171(n+1) through a(5), and grows similarly for n > 5.
Let b(n) = Sum_{j=1..n} a(n); then for n >= 2 it appears that b(n) = round((b(n-1) + 1/2)*e). Verified through n = 10000 (using the approximation Sum_{j=1..k} 1/j = log(k) + gamma + 1/(2*k) - 1/(12*k^2) + 1/(120*k^4) - 1/(252*k^6) + 1/(240*k^8) - ..., where gamma is the Euler-Mascheroni constant, A001620). Cf. A081881. - Jon E. Schoenfield, Jan 10 2020
FORMULA
a(1)=2, a(n) = (min(p) : Sum_{s=r..p} 1/s > 1)-r+1, r=Sum_{k=1..n-1} a(k).
EXAMPLE
a(1)=2 because 1 + 1/2 = 1.5 > 1,
a(2)=5 because 1/3 + 1/4 + 1/5 + 1/6 + 1/7 = 1.0928... > 1,
etc.
PROG
(Python)
x = 0.0
y = 0.0
z = 0.0
for i in range(1, 100000000000000000000000):
y += 1
x = x + 1/i
z = z + 1/i
if x > 1:
print(y)
y = 0
x = 0
(PARI) lista(lim=oo)={my(s=0, p=0); for(i=1, lim, s+=1/i; if(s>1, print1(i-p, ", "); s=0; p=i))} \\ Andrew Howroyd, Jan 08 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Pablo Hueso Merino and Alejandro Argüelles Trujillo, Jan 07 2020
EXTENSIONS
a(25)-a(29) from Jon E. Schoenfield, Jan 10 2020
STATUS
approved