642781 has 4 divisors (see below), whose sum is σ = 670752. Its totient is φ = 614812.

The previous prime is 642779. The next prime is 642791. The reversal of 642781 is 187246.

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 a cyclic number.

It is not a de Polignac number, because 642781 - 2¹ = 642779 is a prime.

It is a super-2 number, since 2×642781² = 826334827922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (642701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13951 + ... + 13996.

It is an arithmetic number, because the mean of its divisors is an integer number (167688).

2⁶⁴²⁷⁸¹ is an apocalyptic number.

It is an amenable number.

642781 is a deficient number, since it is larger than the sum of its proper divisors (27971).

642781 is a wasteful number, since it uses less digits than its factorization.

642781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27970.

The product of its digits is 2688, while the sum is 28.

The square root of 642781 is about 801.7362409172. The cubic root of 642781 is about 86.3020297986.

Subtracting from 642781 its reverse (187246), we obtain a triangular number (455535 = T₉₅₄).

It can be divided in two parts, 6 and 42781, that multiplied together give a triangular number (256686 = T₇₁₆).

The spelling of 642781 in words is "six hundred forty-two thousand, seven hundred eighty-one".