21540661 has 8 divisors (see below), whose sum is σ = 22730400. Its totient is φ = 20356560.

The previous prime is 21540653. The next prime is 21540677. The reversal of 21540661 is 16604512.

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 21540661 - 2³ = 21540653 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 (21540611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8175 + ... + 10483.

It is an arithmetic number, because the mean of its divisors is an integer number (2841300).

Almost surely, 2^21540661 is an apocalyptic number.

It is an amenable number.

21540661 is a deficient number, since it is larger than the sum of its proper divisors (1189739).

21540661 is a wasteful number, since it uses less digits than its factorization.

21540661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2819.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21540661 is about 4641.1917650535. The cubic root of 21540661 is about 278.2400709046.

It can be divided in two parts, 21540 and 661, that added together give a square (22201 = 149²).

The spelling of 21540661 in words is "twenty-one million, five hundred forty thousand, six hundred sixty-one".