• 649 can be written using four 4's:

See also 113.

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649 has 4 divisors (see below), whose sum is σ = 720. Its totient is φ = 580.

The previous prime is 647. The next prime is 653. The reversal of 649 is 946.

649 = 2² + 3² + ... + 12².

It is a happy number.

649 is an esthetic number in base 14, because in such base its adjacent digits differ by 1.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 649 - 2¹ = 647 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13, base 14 and base 16.

It is a nialpdrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (641) 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, 19 + ... + 40.

It is an arithmetic number, because the mean of its divisors is an integer number (180).

2⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

649 is a deficient number, since it is larger than the sum of its proper divisors (71).

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

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

The sum of its prime factors is 70.

The product of its digits is 216, while the sum is 19.

The square root of 649 is about 25.4754784057. The cubic root of 649 is about 8.6579465216.

Subtracting from 649 its sum of digits (19), we obtain a triangular number (630 = T₃₅).

It can be divided in two parts, 64 and 9, that multiplied together give a square (576 = 24²).

The spelling of 649 in words is "six hundred forty-nine", and thus it is an aban number.