21591553 has 2 divisors, whose sum is σ = 21591554. Its totient is φ = 21591552.

The previous prime is 21591541. The next prime is 21591587. The reversal of 21591553 is 35519512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13593969 + 7997584 = 3687^2 + 2828^2 .

It is a cyclic number.

It is not a de Polignac number, because 21591553 - 2⁹ = 21591041 is a prime.

It is not a weakly prime, because it can be changed into another prime (21591523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10795776 + 10795777.

It is an arithmetic number, because the mean of its divisors is an integer number (10795777).

Almost surely, 2^21591553 is an apocalyptic number.

It is an amenable number.

21591553 is a deficient number, since it is larger than the sum of its proper divisors (1).

21591553 is an equidigital number, since it uses as much as digits as its factorization.

21591553 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6750, while the sum is 31.

The square root of 21591553 is about 4646.6711740772. The cubic root of 21591553 is about 278.4590220419.

The spelling of 21591553 in words is "twenty-one million, five hundred ninety-one thousand, five hundred fifty-three".