• Deleting all the even digits from 21557 we obtain a prime of 242 digits.
1557 has 6 divisors (see below), whose sum is σ = 2262. Its totient is φ = 1032.
The previous prime is 1553. The next prime is 1559. The reversal of 1557 is 7551.
It is a happy number.
It can be written as a sum of positive squares in only one way, i.e., 1521 + 36 = 39^2 + 6^2 .
It is not a de Polignac number, because 1557 - 22 = 1553 is a prime.
It is a plaindrome in base 6 and base 10.
It is a nialpdrome in base 12.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (1553) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (5) of ones.
It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 78 + ... + 95.
It is an arithmetic number, because the mean of its divisors is an integer number (377).
It is an amenable number.
1557 is a deficient number, since it is larger than the sum of its proper divisors (705).
1557 is a wasteful number, since it uses less digits than its factorization.
1557 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 179 (or 176 counting only the distinct ones).
The product of its digits is 175, while the sum is 18.
The square root of 1557 is about 39.4588393139. The cubic root of 1557 is about 11.5903407502.
The spelling of 1557 in words is "one thousand, five hundred fifty-seven".
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