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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 ...
where the second term is to be taken as zero if n is not divisible by 4. In particular, for a prime number p we have the explicit formula r 4 (p) = 8(p + 1). [2] Some values of r 4 (n) occur infinitely often as r 4 (n) = r 4 (2 m n) whenever n is even. The values of r 4 (n) can be arbitrarily large: indeed, r 4 (n) is infinitely often larger ...
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
Squares of even numbers are even, and are divisible by 4, since (2n) 2 = 4n 2. Squares of odd numbers are odd, and are congruent to 1 modulo 8, since (2n + 1) 2 = 4n(n + 1) + 1, and n(n + 1) is always even. In other words, all odd square numbers have a remainder of 1 when divided by 8. Every odd perfect square is a centered octagonal number ...
It is an abundant number and also a superabundant number. [2] It is an idoneal number. [3] It is the least common multiple of the numbers from 1 to 8. [4] It is the smallest number divisible by every natural number from 1 to 10, except 9. It is the largest number k such that all coprime quadratic residues modulo k are squares. In this case ...
1646 = number of graphs with 8 nodes and 14 edges [339] 1647 and 1648 are both divisible by cubes [374] 1648 = number of partitions of 34 3 into distinct cubes [375] 1649 = highly cototient number, [43] Leyland number [115] using 4 & 5 (4 5 + 5 4) 1650 = number of cards to build an 33-tier house of cards [164] 1651 = heptagonal number [68]
Cubic reciprocity is a collection of theorems in elementary and algebraic number theory that state conditions under which the congruence x 3 ≡ p (mod q) is solvable; the word "reciprocity" comes from the form of the main theorem, which states that if p and q are primary numbers in the ring of Eisenstein integers, both coprime to 3, the congruence x 3 ≡ p (mod q) is solvable if and only if ...