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The second perfect number. Leonhard Euler (17071783) proved that all even perfect numbers are of the form 2^{n1}(2^{n}  1) where 2^{n}  1 is a Mersenne prime M_{n}. (28#)^{2} + 29 are consecutive primes. [Luhn] 28 is a perfect number expressible as the sum of first five prime numbers, i.e., 2 + 3 + 5 + 7 + 11 = 28. [Gupta] The number of Hadamard matrices of order 28 is prime. [Rupinski] The 28th Fibonacci number plus and minus 28 is prime, i.e., F(28)28 and F(28)+28 are primes. [Opao] (28!+1)/(28+1) is a prime with 28+1 digits. [Silva] The 28th Fibonacci number plus 28^{28} is prime. This is the largest such number less than a thousand. [Opao] 28!+28^28+1 is prime. [Silva] There are 28 (a perfect number) distinct pairs of primes that sum to a thousand: (3, 997), (17, 983), (23, 977), (29, 971), (47, 953), (53, 947), (59, 941), (71, 929), (89, 911), (113, 887), (137, 863), (173, 827), (179, 821), (191, 809), (227, 773), (239, 761), (257, 743), (281, 719), (317, 683), (347, 653), (353, 647), (359, 641), (383, 617), (401, 599), (431, 569), (443, 557), (479, 521), (491, 509). [Loungrides] The current score to beat in King Kong's Prime Numbers Game. Note that 28 is a perfect number. F_{n}^{2}28 is never prime, where F_{n} denotes the nth Fibonacci number. [Poo Sung] 28 is a perfect number expressible as the sum of first five nonprime numbers, i.e., 1 + 4 + 6 + 8 + 9 = 28. [Gaydos]
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