21541661 has 2 divisors, whose sum is σ = 21541662. Its totient is φ = 21541660.

The previous prime is 21541657. The next prime is 21541697. The reversal of 21541661 is 16614512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18232900 + 3308761 = 4270^2 + 1819^2 .

It is a cyclic number.

It is not a de Polignac number, because 21541661 - 2² = 21541657 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21541661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21541631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10770830 + 10770831.

It is an arithmetic number, because the mean of its divisors is an integer number (10770831).

Almost surely, 2^21541661 is an apocalyptic number.

It is an amenable number.

21541661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21541661 is an equidigital number, since it uses as much as digits as its factorization.

21541661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 26.

The square root of 21541661 is about 4641.2994947536. The cubic root of 21541661 is about 278.2443764946.

The spelling of 21541661 in words is "twenty-one million, five hundred forty-one thousand, six hundred sixty-one".