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The basic rule for divisibility by 4 is that if the number formed by the last two digits in a number is divisible by 4, the original number is divisible by 4; [2] [3] this is because 100 is divisible by 4 and so adding hundreds, thousands, etc. is simply adding another number that is divisible by 4. If any number ends in a two digit number that ...
206 is both a nontotient and a noncototient. [1] 206 is an untouchable number. [2] It is the lowest positive integer (when written in English as "two hundred and six") to employ all of the vowels once only, not including Y. The other numbers sharing this property are 230, 250, 260, 602, 640, 5000, 8000, 9000, 26,000, 80,000 and 90,000.
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
About 10 9 hours ago, modern human beings and their ancestors were living in the Stone Age (more precisely, the Middle Paleolithic). (10 9 hours is roughly 114,080 years.) About 10 9 days ago, Australopithecus , an ape-like creature related to an ancestor of modern humans, roamed the African savannas .
The number 28 depicted as 28 balls arranged in a triangular pattern with the number of layers of 7 28 as the sum of four nonzero squares. Twenty-eight is a composite number and the second perfect number as it is the sum of its proper divisors: 1 + 2 + 4 + 7 + 14 = 28 {\displaystyle 1+2+4+7+14=28} .
228 is a refactorable number [1] and a practical number. [2] There are 228 matchings in a ladder graph with five rungs. [3] 228 is the smallest even number n such that the numerator of the nth Bernoulli number is divisible by a nontrivial square number that is relatively prime to n.
In number theory, reversing the digits of a number n sometimes produces another number m that is divisible by n. This happens trivially when n is a palindromic number; the nontrivial reverse divisors are 1089, 2178, 10989, 21978, 109989, 219978, 1099989, 2199978, ... (sequence A008919 in the OEIS).
152 is a refactorable number since it is divisible by the total number of divisors it has, and in base 10 it is divisible by the sum of its digits, making it a Harshad number. The smallest repunit probable prime in base 152 was found in June 2015, it has 589570 digits. [1] The number of surface points on a 6*6*6 cube is 152. [2]