21550561 has 2 divisors, whose sum is σ = 21550562. Its totient is φ = 21550560.

The previous prime is 21550547. The next prime is 21550589. The reversal of 21550561 is 16505512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20611600 + 938961 = 4540^2 + 969^2 .

It is a cyclic number.

It is not a de Polignac number, because 21550561 - 2⁹ = 21550049 is a prime.

It is not a weakly prime, because it can be changed into another prime (21550591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10775280 + 10775281.

It is an arithmetic number, because the mean of its divisors is an integer number (10775281).

Almost surely, 2^21550561 is an apocalyptic number.

It is an amenable number.

21550561 is a deficient number, since it is larger than the sum of its proper divisors (1).

21550561 is an equidigital number, since it uses as much as digits as its factorization.

21550561 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21550561 is about 4642.2581789470. The cubic root of 21550561 is about 278.2826903769.

The spelling of 21550561 in words is "twenty-one million, five hundred fifty thousand, five hundred sixty-one".