21661501 has 16 divisors (see below), whose sum is σ = 23592960. Its totient is φ = 19822320.

The previous prime is 21661499. The next prime is 21661517. The reversal of 21661501 is 10516612.

It is not a de Polignac number, because 21661501 - 2¹ = 21661499 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 (21661531) 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 15 ways as a sum of consecutive naturals, for example, 113316 + ... + 113506.

It is an arithmetic number, because the mean of its divisors is an integer number (1474560).

Almost surely, 2^21661501 is an apocalyptic number.

It is an amenable number.

21661501 is a deficient number, since it is larger than the sum of its proper divisors (1931459).

21661501 is a wasteful number, since it uses less digits than its factorization.

21661501 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 384.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21661501 is about 4654.1917665691. The cubic root of 21661501 is about 278.7593965476.

The spelling of 21661501 in words is "twenty-one million, six hundred sixty-one thousand, five hundred one".