21660765 has 32 divisors (see below), whose sum is σ = 40212480. Its totient is φ = 9751104.

The previous prime is 21660761. The next prime is 21660791. The reversal of 21660765 is 56706612.

21660765 = T₁₀₉₅ + T₁₀₉₆ + ... + T₁₁₂₉.

It is not a de Polignac number, because 21660765 - 2² = 21660761 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660761) 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 31 ways as a sum of consecutive naturals, for example, 5496 + ... + 8574.

It is an arithmetic number, because the mean of its divisors is an integer number (1256640).

Almost surely, 2^21660765 is an apocalyptic number.

It is an amenable number.

21660765 is a deficient number, since it is larger than the sum of its proper divisors (18551715).

21660765 is a wasteful number, since it uses less digits than its factorization.

21660765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3161.

The product of its (nonzero) digits is 15120, while the sum is 33.

The square root of 21660765 is about 4654.1126973893. The cubic root of 21660765 is about 278.7562393450.

The spelling of 21660765 in words is "twenty-one million, six hundred sixty thousand, seven hundred sixty-five".