21557447 has 2 divisors, whose sum is σ = 21557448. Its totient is φ = 21557446.

The previous prime is 21557407. The next prime is 21557453. The reversal of 21557447 is 74475512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21557447 - 2⁶ = 21557383 is a prime.

It is a Chen prime.

It is equal to p_1362968 and since 21557447 and 1362968 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

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

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778723 + 10778724.

It is an arithmetic number, because the mean of its divisors is an integer number (10778724).

Almost surely, 2^21557447 is an apocalyptic number.

21557447 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557447 is an equidigital number, since it uses as much as digits as its factorization.

21557447 is an evil number, because the sum of its binary digits is even.

The product of its digits is 39200, while the sum is 35.

The square root of 21557447 is about 4642.9997846220. Note that the first 3 decimals coincide. The cubic root of 21557447 is about 278.3123268914.

The spelling of 21557447 in words is "twenty-one million, five hundred fifty-seven thousand, four hundred forty-seven".