• 649 can be written using four 4's:
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 a Duffinian number.
It is a plaindrome in base 13, base 14 and base 16.
It is a nialpdrome in base 11.
2649 is an apocalyptic number.
It is an amenable number.
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 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).
The spelling of 649 in words is "six hundred forty-nine", and thus it is an aban number.