21587921 has 2 divisors, whose sum is σ = 21587922. Its totient is φ = 21587920.

The previous prime is 21587893. The next prime is 21587941. The reversal of 21587921 is 12978512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21520321 + 67600 = 4639^2 + 260^2 .

It is a cyclic number.

It is not a de Polignac number, because 21587921 - 2¹⁰ = 21586897 is a prime.

It is equal to p_1364786 and since 21587921 and 1364786 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 (21587941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10793960 + 10793961.

It is an arithmetic number, because the mean of its divisors is an integer number (10793961).

Almost surely, 2^21587921 is an apocalyptic number.

It is an amenable number.

21587921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21587921 is an equidigital number, since it uses as much as digits as its factorization.

21587921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10080, while the sum is 35.

The square root of 21587921 is about 4646.2803402292. The cubic root of 21587921 is about 278.4434076041.

The spelling of 21587921 in words is "twenty-one million, five hundred eighty-seven thousand, nine hundred twenty-one".