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  2. Missing dollar riddle - Wikipedia

    en.wikipedia.org/wiki/Missing_dollar_riddle

    8) 9 + 9 + 9 -2 = 25 + 2 -2 (adding -2 to both sides of the equation to cancel the +2 on the right side, which means the bellhop returned the tip or gave a discount of $2) 9) 9 + 9 + 9 - 2 = 25 10) 27 - 2 = 25 11) 25 = 25. The puzzle should subtract the bellhop's tip from the $27 rather than add it. History. There are many variants of the puzzle.

  3. List of prime numbers - Wikipedia

    en.wikipedia.org/wiki/List_of_prime_numbers

    Weakly prime numbers. Primes that having any one of their (base 10) digits changed to any other value will always result in a composite number. 294001, 505447, 584141, 604171, 971767, 1062599, 1282529, 1524181, 2017963, 2474431, 2690201, 3085553, 3326489, 4393139 ( OEIS : A050249 )

  4. Apéry's constant - Wikipedia

    en.wikipedia.org/wiki/Apéry's_constant

    In mathematics, Apéry's constant is the sum of the reciprocals of the positive cubes. That is, it is defined as the number. where ζ is the Riemann zeta function. It has an approximate value of [1] ζ(3) ≈ 1.20205 69031 59594 28539 97381 61511 44999 07649 86292 … (sequence A002117 in the OEIS ). The constant is named after Roger Apéry.

  5. Unary numeral system - Wikipedia

    en.wikipedia.org/wiki/Unary_numeral_system

    The unary numeral system is the simplest numeral system to represent natural numbers: to represent a number N, a symbol representing 1 is repeated N times. [2] In the unary system, the number 0 (zero) is represented by the empty string , that is, the absence of a symbol.

  6. Particular values of the Riemann zeta function - Wikipedia

    en.wikipedia.org/wiki/Particular_values_of_the...

    It is known that ζ(3) is irrational (Apéry's theorem) and that infinitely many of the numbers ζ(2n + 1) : n ∈ , are irrational. There are also results on the irrationality of values of the Riemann zeta function at the elements of certain subsets of the positive odd integers; for example, at least one of ζ (5), ζ (7), ζ (9), or ζ (11 ...

  7. 1 + 2 + 3 + 4 + ⋯ - Wikipedia

    en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E...

    The partial sums of the series 1 + 2 + 3 + 4 + 5 + 6 + ⋯ are 1, 3, 6, 10, 15, etc.The nth partial sum is given by a simple formula: = = (+). This equation was known ...

  8. 800 (number) - Wikipedia

    en.wikipedia.org/wiki/800_(number)

    855 = 3 2 × 5 × 19, decagonal number, centered cube number. country calling code for Cambodia; 856 = 2 3 × 107, nonagonal number, centered pentagonal number, happy number, refactorable number. country calling code for Laos; 857 = prime number, sum of three consecutive primes (281 + 283 + 293), Chen prime, Eisenstein prime with no imaginary part

  9. 168 (number) - Wikipedia

    en.wikipedia.org/wiki/168_(number)

    168 is also coefficient four in the expansion of Eisenstein series, which also includes 144 and 96 (or 48 × 2) as the fifth and third coefficients, respectively — these have a sum of 240, which follows 144 and 187 in the list of successive composites (+) = (); cf. the latter holds a sum-of-divisors of 216 = 6 3, which is the 168th composite ...