661742021 has 8 divisors (see below), whose sum is σ = 666463200. Its totient is φ = 657029232.

The previous prime is 661741991. The next prime is 661742023. The reversal of 661742021 is 120247166.

661742021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 661742021 - 2⁶ = 661741957 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661742023) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 316646 + ... + 318728.

It is an arithmetic number, because the mean of its divisors is an integer number (83307900).

Almost surely, 2^661742021 is an apocalyptic number.

It is an amenable number.

661742021 is a deficient number, since it is larger than the sum of its proper divisors (4721179).

661742021 is a wasteful number, since it uses less digits than its factorization.

661742021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4195.

The product of its (nonzero) digits is 4032, while the sum is 29.

The square root of 661742021 is about 25724.3468527386. The cubic root of 661742021 is about 871.4241092194.

Adding to 661742021 its reverse (120247166), we get a palindrome (781989187).

The spelling of 661742021 in words is "six hundred sixty-one million, seven hundred forty-two thousand, twenty-one".