ABC172 D - Sum of Divisors

提出

code: python

n = int(input())

def make_divisors(n):

lower_divisors , upper_divisors = [], []

i = 1

while i*i <= n:

if n % i == 0:

lower_divisors.append(i)

if i != n // i:

upper_divisors.append(n//i)

i += 1

ans = 0

# どこかでメモ化しないといけない

for i in range(1, n+1):

ans += i * len(make_divisors(i))

print(ans)

解答

https://scrapbox.io/files/61ca4976fa875f001d68d464.png

縦の個数がf(K)

code: python

n = int(input())

ans = 0

# 1で割り切れる数の和は1+2+...+8

# 2で割り切れる数の和は2+4+...+8

for i in range(1, n+1):

x, y = i, (n//i)*i

# 等差数列の和 = (項数*(初項+末項)) / 2

ans += ((n//i) * (x + y) // 2)

print(ans)