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15: It is divisible by 3 and by 5. [6] 390: it is divisible by 3 and by 5. 16: If the thousands digit is even, the number formed by the last three digits must be divisible by 16. 254,176: 176. If the thousands digit is odd, the number formed by the last three digits must be 8 times an odd number. 3408: 408 = 8 × 51. Add the last two digits to ...
That is, although 360 and 2520 both have more divisors than any number twice themselves, 2520 is the lowest number divisible by both 1 to 9 and 1 to 10, whereas 360 is not the lowest number divisible by 1 to 6 (which 60 is) and is not divisible by 1 to 7 (which 420 is).
d() is the number of positive divisors of n, including 1 and n itself; σ() is the sum of the positive divisors of n, including 1 and n itselfs() is the sum of the proper divisors of n, including 1 but not n itself; that is, s(n) = σ(n) − n
Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the years 1600 and 2000 are. [8] 1800 calendar, showing that February had only 28 days
The number 18 is a harshad number in base 10, because the sum of the digits 1 and 8 is 9, and 18 is divisible by 9.; The Hardy–Ramanujan number (1729) is a harshad number in base 10, since it is divisible by 19, the sum of its digits (1729 = 19 × 91).
12 (twelve) is the natural number following 11 and preceding 13. Twelve is the 3rd superior highly composite number , [ 1 ] the 3rd colossally abundant number , [ 2 ] the 5th highly composite number , and is divisible by the numbers from 1 to 4 , and 6 , a large number of divisors comparatively.
The smallest abundant number not divisible by 2 or by 3 is 5391411025 whose distinct prime factors are 5, 7, 11, 13, 17, 19, 23, and 29 (sequence A047802 in the OEIS). An algorithm given by Iannucci in 2005 shows how to find the smallest abundant number not divisible by the first k primes. [1]
The solar cycle is a 28-year cycle of the Julian calendar, and 400-year cycle of the Gregorian calendar with respect to the week.It occurs because leap years occur every 4 years, typically observed by adding a day to the month of February, making it February 29th.