649821 has 4 divisors (see below), whose sum is σ = 866432. Its totient is φ = 433212.

The previous prime is 649813. The next prime is 649829. The reversal of 649821 is 128946.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (649813) and next prime (649829).

It is not a de Polignac number, because 649821 - 2³ = 649813 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (649829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 108301 + ... + 108306.

It is an arithmetic number, because the mean of its divisors is an integer number (216608).

2⁶⁴⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

649821 is a deficient number, since it is larger than the sum of its proper divisors (216611).

649821 is a wasteful number, since it uses less digits than its factorization.

649821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216610.

The product of its digits is 3456, while the sum is 30.

The square root of 649821 is about 806.1147560987. The cubic root of 649821 is about 86.6159581733.

The spelling of 649821 in words is "six hundred forty-nine thousand, eight hundred twenty-one".