1105 (eleven hundred [and] five, or one thousand one hundred [and] five) is the natural number following 1104 and preceding 1106.
Mathematical properties 1105 is the smallest positive integer that is a sum of two positive squares in exactly four different ways, a property that can be connected (via the sum of two squares theorem) to its factorization as the product of the three smallest prime numbers that are congruent to 1 modulo 4. It is also the second-smallest Carmichael number, after 561, one of the first four Carmichael numbers identified by R. D. Carmichael in his 1910 paper introducing this concept. It is also a Fermat pseudoprime, a decagonal number, and a centered square number.
It is a member of the Moser–de Bruijn sequence of sums of distinct powers of four.
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