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Natural number
555 (five hundred [and] fifty-five) is the natural number following 554 and preceding 556.
555 is a sphenic number. In base 10, it is a repdigit, and because it is divisible by the sum of its digits, it is a Harshad number. It is also a Harshad number in binary, base 11, base 13 and hexadecimal.
555 is a Harshad number as 555 ÷ (5+5+5) is 555 ÷ 15 is 37.[1] Also, 555 is unique because it is not just a multiple of 5+5+5 (15) but that 15 is divisible by its triangular order.
It is the sum of the first triplet of three-digit permutable primes in decimal:
It is the twenty-sixth number such that its Euler totient (288) is equal to the totient value of its sum-of-divisors: φ ( 555 ) = φ ( σ ( 555 ) ) {\displaystyle \varphi (555)=\varphi (\sigma (555))} .[2]
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