1661292720 has 80 divisors (see below), whose sum is σ = 5722237920. Its totient is φ = 443010816.

The previous prime is 1661292701. The next prime is 1661292761. The reversal of 1661292720 is 272921661.

1661292720 is a `hidden beast` number, since 16 + 612 + 9 + 2 + 7 + 20 = 666.

It is a tau number, because it is divible by the number of its divisors (80).

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

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 382399 + ... + 386718.

It is an arithmetic number, because the mean of its divisors is an integer number (71527974).

Almost surely, 2^1661292720 is an apocalyptic number.

1661292720 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

1661292720 is an abundant number, since it is smaller than the sum of its proper divisors (4060945200).

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

1661292720 is a wasteful number, since it uses less digits than its factorization.

1661292720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 769139 (or 769127 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 1661292720 is about 40758.9587698214. The cubic root of 1661292720 is about 1184.3554257689.

The spelling of 1661292720 in words is "one billion, six hundred sixty-one million, two hundred ninety-two thousand, seven hundred twenty".