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Formula for primes
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==A function that represents all primes== Given the constant <math>f_1 = 2.920050977316\ldots</math> {{OEIS|A249270}}, for <math>n \ge 2</math>, define the sequence {{NumBlk|:|<math> f_n = \left\lfloor f_{n-1} \right\rfloor (f_{n-1} - \left\lfloor f_{n-1} \right\rfloor + 1 ) </math>|{{EquationRef|1}}}} where <math>\left\lfloor\ \right\rfloor</math> is the [[floor function]]. Then for <math>n \ge 1</math>, <math>\left\lfloor f_{n} \right\rfloor</math> equals the <math>n</math>th prime: <math>\left\lfloor f_1 \right\rfloor = 2</math>, <math>\left\lfloor f_2 \right\rfloor = 3</math>, <math>\left\lfloor f_3 \right\rfloor = 5</math>, etc. <ref name="FridmanEtAl">{{citation | doi = 10.1080/00029890.2019.1530554 | first1=Dylan | last1=Fridman | first2=Juli | last2=Garbulsky | first3=Bruno | last3=Glecer | first4=James | last4=Grime | first5=Massi | last5=Tron Florentin | title = A Prime-Representing Constant | journal = American Mathematical Monthly | volume = 126 | issue = 1 | pages = 70β73 | publisher = [[Mathematical Association of America]] | location = Washington, DC | year = 2019| arxiv=2010.15882 | s2cid=127727922 }} </ref> The initial constant <math>f_1 = 2.920050977316</math> given in the article is precise enough for equation ({{EquationNote|1}}) to generate the primes through 37, the <math>12</math>th prime. The ''exact'' value of <math>f_1</math> that generates ''all'' primes is given by the rapidly-converging [[Series (mathematics)|series]] :<math> f_1 = \sum_{n=1}^\infty \frac{p_n - 1}{P_n} = \frac{2 - 1}{1} + \frac{3 - 1}{2} + \frac{5 - 1}{2 \cdot 3} + \frac{7 - 1}{2 \cdot 3 \cdot 5} + \cdots, </math> where <math>p_n</math> is the <math>n</math>th prime, and <math>P_n</math> is the product of all primes less than <math>p_n</math>. The more digits of <math>f_1</math> that we know, the more primes equation ({{EquationNote|1}}) will generate. For example, we can use 25 terms in the series, using the 25 primes less than 100, to calculate the following more precise approximation: : <math>f_1 \simeq 2.920050977316134712092562917112019.</math> This has enough digits for equation ({{EquationNote|1}}) to yield again the 25 primes less than 100. As with Mills' formula and Wright's formula above, in order to generate a longer list of primes, we need to start by knowing more digits of the initial constant, <math>f_1</math>, which in this case requires a longer list of primes in its calculation.
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