21591541 has 2 divisors, whose sum is σ = 21591542. Its totient is φ = 21591540.

The previous prime is 21591539. The next prime is 21591553. The reversal of 21591541 is 14519512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11029041 + 10562500 = 3321^2 + 3250^2 .

It is a cyclic number.

It is not a de Polignac number, because 21591541 - 2¹ = 21591539 is a prime.

Together with 21591539, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21591041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10795770 + 10795771.

It is an arithmetic number, because the mean of its divisors is an integer number (10795771).

Almost surely, 2^21591541 is an apocalyptic number.

It is an amenable number.

21591541 is a deficient number, since it is larger than the sum of its proper divisors (1).

21591541 is an equidigital number, since it uses as much as digits as its factorization.

21591541 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1800, while the sum is 28.

The square root of 21591541 is about 4646.6698828301. The cubic root of 21591541 is about 278.4589704552.

The spelling of 21591541 in words is "twenty-one million, five hundred ninety-one thousand, five hundred forty-one".