21557401 has 2 divisors, whose sum is σ = 21557402. Its totient is φ = 21557400.

The previous prime is 21557387. The next prime is 21557407. The reversal of 21557401 is 10475512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13286025 + 8271376 = 3645^2 + 2876^2 .

It is a cyclic number.

It is not a de Polignac number, because 21557401 - 2¹¹ = 21555353 is a prime.

It is not a weakly prime, because it can be changed into another prime (21557407) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778700 + 10778701.

It is an arithmetic number, because the mean of its divisors is an integer number (10778701).

Almost surely, 2^21557401 is an apocalyptic number.

It is an amenable number.

21557401 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557401 is an equidigital number, since it uses as much as digits as its factorization.

21557401 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 21557401 is about 4642.9948309254. The cubic root of 21557401 is about 278.3121289339.

The spelling of 21557401 in words is "twenty-one million, five hundred fifty-seven thousand, four hundred one".