21663761 has 8 divisors (see below), whose sum is σ = 25557504. Its totient is φ = 17969760.

The previous prime is 21663751. The next prime is 21663767. The reversal of 21663761 is 16736612.

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 21663761 - 2¹⁴ = 21647377 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21663767) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 49700 + ... + 50133.

It is an arithmetic number, because the mean of its divisors is an integer number (3194688).

Almost surely, 2^21663761 is an apocalyptic number.

It is an amenable number.

21663761 is a deficient number, since it is larger than the sum of its proper divisors (3893743).

21663761 is an equidigital number, since it uses as much as digits as its factorization.

21663761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99871.

The product of its digits is 9072, while the sum is 32.

The square root of 21663761 is about 4654.4345521234. The cubic root of 21663761 is about 278.7690907716.

The spelling of 21663761 in words is "twenty-one million, six hundred sixty-three thousand, seven hundred sixty-one".