642978 has 54 divisors (see below), whose sum is σ = 1682811.
Its totient is φ = 183708.
The previous prime is 642977. The next prime is 642997. The reversal of 642978 is 879246.
642978 is a `hidden beast` number, since 642 + 9 + 7 + 8 = 666.
It can be written as a sum of positive squares in only one way, i.e., 321489 + 321489 = 567^2 + 567^2
It is a tau number, because it is divible by the number of its divisors (54).
It is an ABA number since it can be written as A⋅BA, here for A=2, B=567.
Its product of digits (24192) is a multiple of the sum of its prime divisors (12).
It is not an unprimeable number, because it can be changed into a prime (642973) by changing a digit.
It is a pernicious number, because its binary representation contains a prime number (11) of ones.
It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 91851 + ... + 91857.
642978 is a Friedman number, since it can be written as 98*(7-4)^(6+2), using all its digits and the basic arithmetic operations.
2642978 is an apocalyptic number.
It is a practical number, because each smaller number is the sum of distinct divisors of 642978
642978 is an abundant number, since it is smaller than the sum of its proper divisors (1039833).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
642978 is an frugal number, since it uses more digits than its factorization.
642978 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 40 (or 12 counting only the distinct ones).
The product of its digits is 24192, while the sum is 36.
The square root of 642978 is about 801.8590898655.
The cubic root of 642978 is about 86.3108455349.
The spelling of 642978 in words is "six hundred forty-two thousand, nine hundred seventy-eight".