21021457 has 2 divisors, whose sum is σ = 21021458. Its totient is φ = 21021456.

The previous prime is 21021449. The next prime is 21021463. The reversal of 21021457 is 75412012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17338896 + 3682561 = 4164^2 + 1919^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021457 - 2³ = 21021449 is a prime.

It is equal to p_1331257 and since 21021457 and 1331257 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21021157) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510728 + 10510729.

It is an arithmetic number, because the mean of its divisors is an integer number (10510729).

Almost surely, 2^21021457 is an apocalyptic number.

It is an amenable number.

21021457 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021457 is an equidigital number, since it uses as much as digits as its factorization.

21021457 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21021457 is about 4584.9162478719. The cubic root of 21021457 is about 275.9863511069.

Adding to 21021457 its reverse (75412012), we get a palindrome (96433469).

The spelling of 21021457 in words is "twenty-one million, twenty-one thousand, four hundred fifty-seven".