*
n*(n+1)//2

ssh=(cuoi-dau)//khoang cach +1

tong=(cuoi + dau) * ssh //2

def ktngt(n):
if n<2:
return False
for i in range(1,int(n**0.5)+1):
if n%i==0:
return False
return True

cong thuc ssh and tsh
ssh=(c-d)//kc+1
tong=(c+d)*ssh//2

def ktsnt(n):
if n<2:
return False
for i in range (2,int(n**0.5)+1):
if n%i==0:
return False
return True

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Nguyên Khôi mãi ngu

[user:]enter username here((\(strong text\)\)\)