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+ Levy's conjecture (1963) states that all odd numbers greater than or equal to 7 are the sum of a prime plus twice a prime. It was named after Hyman Levy, who was apparently unaware that the conjecture was first stated by Émile Lemoine in 1894. [Capelle]

+ The smallest prime p that yields a number of the form pp when multiplied by the next prime. [Capelle]

+ The only prime p such that pi(p2) < (pi(p))2. [Capelle]

+ There are 72 natural numbers n such that n is equal to the number of 7's in the decimal digits of all numbers smaller or equal to n. [Capelle]

+ The Pollock octahedral numbers conjecture (1850) states that every number can be written as the sum of at most seven octahedral numbers. Frederick Pollock, better known as a lawyer and politician, was a contributor of papers on mathematics to the Royal Society. [Capelle]

+ The largest known prime number that is not the sum of a triangular number, a square and a cube, all of them greater than or equal to 1. [Capelle]

+ Seven prime numbers cannot be written as a sum of squares of primes. Note that 7 is one of them and divides their sum. [Capelle]

+ The largest known prime number p for which the decimal expansion of pp does not contain any pair of consecutive equal digits. [Capelle]

+ There are 7 known natural numbers n such that n is the sum of two consecutive primes but not the sum of two sums of two consecutive primes. [Capelle]

+ The number of capital letters of English alphabet with no symmetry (F, G, J, L, P, Q, R). Note that the letters P, Q and R are often used to represent the primes. [Capelle]

+ The number of strobogrammatic capital letters of the English alphabet (H, I, N, O, S, X, Z). The word strobogrammatic begins with S, the only strobogrammatic letter with a prime index. [Capelle]

+ Giraffes have seven neck bones, which is the same as humans and most other mammals but longer. [Capelle]

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