1642721661 has 32 divisors (see below), whose sum is σ = 2798443520. Its totient is φ = 932921712.

The previous prime is 1642721609. The next prime is 1642721677. The reversal of 1642721661 is 1661272461.

1642721661 is a `hidden beast` number, since 1 + 642 + 7 + 2 + 1 + 6 + 6 + 1 = 666.

It is not a de Polignac number, because 1642721661 - 2²³ = 1634333053 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1642721681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4146 + ... + 57468.

It is an arithmetic number, because the mean of its divisors is an integer number (87451360).

Almost surely, 2^1642721661 is an apocalyptic number.

It is an amenable number.

1642721661 is a deficient number, since it is larger than the sum of its proper divisors (1155721859).

1642721661 is a wasteful number, since it uses less digits than its factorization.

1642721661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53502 (or 53496 counting only the distinct ones).

The product of its digits is 24192, while the sum is 36.

The square root of 1642721661 is about 40530.5028466216. The cubic root of 1642721661 is about 1179.9257017760.

The spelling of 1642721661 in words is "one billion, six hundred forty-two million, seven hundred twenty-one thousand, six hundred sixty-one".