21541721 has 2 divisors, whose sum is σ = 21541722. Its totient is φ = 21541720.

The previous prime is 21541717. The next prime is 21541727. The reversal of 21541721 is 12714512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18156121 + 3385600 = 4261^2 + 1840^2 .

It is a cyclic number.

It is not a de Polignac number, because 21541721 - 2² = 21541717 is a prime.

It is not a weakly prime, because it can be changed into another prime (21541727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10770860 + 10770861.

It is an arithmetic number, because the mean of its divisors is an integer number (10770861).

Almost surely, 2^21541721 is an apocalyptic number.

It is an amenable number.

21541721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21541721 is an equidigital number, since it uses as much as digits as its factorization.

21541721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 560, while the sum is 23.

The square root of 21541721 is about 4641.3059584561. The cubic root of 21541721 is about 278.2446348258.

The spelling of 21541721 in words is "twenty-one million, five hundred forty-one thousand, seven hundred twenty-one".