21000261 has 4 divisors (see below), whose sum is σ = 28000352. Its totient is φ = 14000172.

The previous prime is 21000251. The next prime is 21000269. The reversal of 21000261 is 16200012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21000261 - 2⁵ = 21000229 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000269) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3500041 + ... + 3500046.

It is an arithmetic number, because the mean of its divisors is an integer number (7000088).

Almost surely, 2^21000261 is an apocalyptic number.

It is an amenable number.

21000261 is a deficient number, since it is larger than the sum of its proper divisors (7000091).

21000261 is an equidigital number, since it uses as much as digits as its factorization.

21000261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7000090.

The product of its (nonzero) digits is 24, while the sum is 12.

The square root of 21000261 is about 4582.6041723020. The cubic root of 21000261 is about 275.8935606162.

Adding to 21000261 its reverse (16200012), we get a palindrome (37200273).

The spelling of 21000261 in words is "twenty-one million, two hundred sixty-one", and thus it is an aban number.