555 (number)
Template:About Template:One source Template:Infobox number 555 (five hundred [and] fifty-five) is the natural number following 554 and preceding 556.
In mathematics
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.<ref>Template:Cite web</ref> 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:
- <math>113 + 131 + 311 = 555</math>.
It is the twenty-sixth number such that its Euler totient (288) is equal to the totient value of its sum-of-divisors: <math>\varphi(555) = \varphi(\sigma(555))</math>.<ref>Template:Cite OEIS</ref>