21721668385 has 16 divisors (see below), whose sum is σ = 26178109056. Its totient is φ = 17302664448.

The previous prime is 21721668359. The next prime is 21721668401. The reversal of 21721668385 is 58386612712.

21721668385 = T₄₁₄ + T₄₁₅ + ... + T₅₀₇₀.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21721668385 - 2¹³ = 21721660193 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4661977 + ... + 4666633.

It is an arithmetic number, because the mean of its divisors is an integer number (1636131816).

Almost surely, 2^21721668385 is an apocalyptic number.

It is an amenable number.

21721668385 is a deficient number, since it is larger than the sum of its proper divisors (4456440671).

21721668385 is a wasteful number, since it uses less digits than its factorization.

21721668385 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8472.

The product of its digits is 967680, while the sum is 49.

The spelling of 21721668385 in words is "twenty-one billion, seven hundred twenty-one million, six hundred sixty-eight thousand, three hundred eighty-five".