21615641 has 2 divisors, whose sum is σ = 21615642. Its totient is φ = 21615640.

The previous prime is 21615637. The next prime is 21615647. The reversal of 21615641 is 14651612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18361225 + 3254416 = 4285^2 + 1804^2 .

It is a cyclic number.

It is not a de Polignac number, because 21615641 - 2² = 21615637 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21615641.

It is not a weakly prime, because it can be changed into another prime (21615647) 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 as a sum of consecutive naturals, namely, 10807820 + 10807821.

It is an arithmetic number, because the mean of its divisors is an integer number (10807821).

Almost surely, 2^21615641 is an apocalyptic number.

It is an amenable number.

21615641 is a deficient number, since it is larger than the sum of its proper divisors (1).

21615641 is an equidigital number, since it uses as much as digits as its factorization.

21615641 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 26.

The square root of 21615641 is about 4649.2624146202. The cubic root of 21615641 is about 278.5625351783.

The spelling of 21615641 in words is "twenty-one million, six hundred fifteen thousand, six hundred forty-one".