21354721 has 2 divisors, whose sum is σ = 21354722. Its totient is φ = 21354720.

The previous prime is 21354667. The next prime is 21354797. The reversal of 21354721 is 12745312.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17969121 + 3385600 = 4239^2 + 1840^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21354721 is a prime.

It is not a weakly prime, because it can be changed into another prime (21351721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10677360 + 10677361.

It is an arithmetic number, because the mean of its divisors is an integer number (10677361).

Almost surely, 2^21354721 is an apocalyptic number.

It is an amenable number.

21354721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21354721 is an equidigital number, since it uses as much as digits as its factorization.

21354721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1680, while the sum is 25.

The square root of 21354721 is about 4621.1168563454. The cubic root of 21354721 is about 277.4371624081.

The spelling of 21354721 in words is "twenty-one million, three hundred fifty-four thousand, seven hundred twenty-one".