661968 has 30 divisors (see below), whose sum is σ = 1852994. Its totient is φ = 220608.

The previous prime is 661961. The next prime is 661987. The reversal of 661968 is 869166.

It can be written as a sum of positive squares in only one way, i.e., 419904 + 242064 = 648^2 + 492^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661961) by changing a digit.

661968 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2155 + ... + 2442.

2⁶⁶¹⁹⁶⁸ is an apocalyptic number.

It is an amenable number.

661968 is an abundant number, since it is smaller than the sum of its proper divisors (1191026).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661968 is a wasteful number, since it uses less digits than its factorization.

661968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4611 (or 4602 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 661968 is about 813.6141591688. The cubic root of 661968 is about 87.1523292451.

Subtracting from 661968 its product of digits (15552), we obtain a square (646416 = 804²).

The spelling of 661968 in words is "six hundred sixty-one thousand, nine hundred sixty-eight".