21036561 has 32 divisors (see below), whose sum is σ = 34771968. Its totient is φ = 11016000.

The previous prime is 21036539. The next prime is 21036563. The reversal of 21036561 is 16563012.

It is not a de Polignac number, because 21036561 - 2¹⁰ = 21035537 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21036563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 68370 + ... + 68676.

It is an arithmetic number, because the mean of its divisors is an integer number (1086624).

Almost surely, 2^21036561 is an apocalyptic number.

21036561 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21036561 is a deficient number, since it is larger than the sum of its proper divisors (13735407).

21036561 is a wasteful number, since it uses less digits than its factorization.

21036561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 581.

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21036561 is about 4586.5630923383. The cubic root of 21036561 is about 276.0524343773.

Adding to 21036561 its reverse (16563012), we get a palindrome (37599573).

The spelling of 21036561 in words is "twenty-one million, thirty-six thousand, five hundred sixty-one".