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  2. Euler's totient function - Wikipedia

    en.wikipedia.org/wiki/Euler's_totient_function

    If n is a power of an odd prime number the formula for the totient says its totient can be a power of two only if n is a first power and n − 1 is a power of 2. The primes that are one more than a power of 2 are called Fermat primes, and only five are known: 3, 5, 17, 257, and 65537. Fermat and Gauss knew of these.

  3. Formula for primes - Wikipedia

    en.wikipedia.org/wiki/Formula_for_primes

    However, it does not contain all the prime numbers, since the terms gcd(n + 1, a n) are always odd and so never equal to 2. 587 is the smallest prime (other than 2) not appearing in the first 10,000 outcomes that are different from 1. Nevertheless, in the same paper it was conjectured to contain all odd primes, even though it is rather inefficient.

  4. Harmonic number - Wikipedia

    en.wikipedia.org/wiki/Harmonic_number

    The first 40 harmonic numbers n ... is an odd number while the denominator of is an even ... The harmonic numbers appear in several calculation formulas, ...

  5. List of sums of reciprocals - Wikipedia

    en.wikipedia.org/wiki/List_of_sums_of_reciprocals

    The n-th harmonic number, which is the sum of the reciprocals of the first n positive integers, is never an integer except for the case n = 1. Moreover, József Kürschák proved in 1918 that the sum of the reciprocals of consecutive natural numbers (whether starting from 1 or not) is never an integer.

  6. List of prime numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_prime_numbers

    Subsets of the prime numbers may be generated with various formulas for primes. The first 1000 ... for some prime number n. 3 ... Of the form k×2 n + 1, with odd k ...

  7. Faulhaber's formula - Wikipedia

    en.wikipedia.org/wiki/Faulhaber's_formula

    Since a = n(n + 1)/2, these formulae show that for an odd power (greater than 1), the sum is a polynomial in n having factors n 2 and (n + 1) 2, while for an even power the polynomial has factors n, n + 1/2 and n + 1.

  8. Bernoulli number - Wikipedia

    en.wikipedia.org/wiki/Bernoulli_number

    In mathematics, the Bernoulli numbers B n are a sequence of rational numbers which occur frequently in analysis.The Bernoulli numbers appear in (and can be defined by) the Taylor series expansions of the tangent and hyperbolic tangent functions, in Faulhaber's formula for the sum of m-th powers of the first n positive integers, in the Euler–Maclaurin formula, and in expressions for certain ...

  9. Gould's sequence - Wikipedia

    en.wikipedia.org/wiki/Gould's_sequence

    count all odd numbers in the first n rows of Pascal's triangle. These numbers grow proportionally to n log 2 ⁡ 3 ≈ n 1.585 {\displaystyle n^{\log _{2}3}\approx n^{1.585}} , but with a constant of proportionality that oscillates between 0.812556... and 1, periodically as a function of log n .