21647621 has 2 divisors, whose sum is σ = 21647622. Its totient is φ = 21647620.

The previous prime is 21647617. The next prime is 21647629. The reversal of 21647621 is 12674612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21031396 + 616225 = 4586^2 + 785^2 .

It is a cyclic number.

It is not a de Polignac number, because 21647621 - 2² = 21647617 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21647629) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10823810 + 10823811.

It is an arithmetic number, because the mean of its divisors is an integer number (10823811).

Almost surely, 2^21647621 is an apocalyptic number.

It is an amenable number.

21647621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21647621 is an equidigital number, since it uses as much as digits as its factorization.

21647621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4032, while the sum is 29.

The square root of 21647621 is about 4652.7003986932. The cubic root of 21647621 is about 278.6998437780.

The spelling of 21647621 in words is "twenty-one million, six hundred forty-seven thousand, six hundred twenty-one".