The book is now available! 91
(another Prime Pages' Curiosity)
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The nth Prime Page will now find any of the first 2.623˙1015 primes or π(x) for x up to 1017.

+ 91 is pseudoprime to 35 bases less than 91. [Redman]

+ 10n + 91 {+ 0, + 2} are twin primes for n = 1, 2, 3 and 4. [Luhn]

+ 91 is the smallest non-trivial odd composite (that is, its prime factors [7, 13] are not, at first glance, obvious). Every smaller odd composite is either a familiar square, ends in 5, has a digit sum that is a multiple of 3, or is obviously divisible by 11.

+ 91 is the smallest pseudoprime satisfying the congruence 3^n = 3modn.

(There is one curio for this number that has not yet been approved by an editor.)

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