21640651 has 2 divisors, whose sum is σ = 21640652. Its totient is φ = 21640650.

The previous prime is 21640637. The next prime is 21640667. The reversal of 21640651 is 15604612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21640651 - 2¹³ = 21632459 is a prime.

It is not a weakly prime, because it can be changed into another prime (21640621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10820325 + 10820326.

It is an arithmetic number, because the mean of its divisors is an integer number (10820326).

Almost surely, 2^21640651 is an apocalyptic number.

21640651 is a deficient number, since it is larger than the sum of its proper divisors (1).

21640651 is an equidigital number, since it uses as much as digits as its factorization.

21640651 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21640651 is about 4651.9513110092. The cubic root of 21640651 is about 278.6699290754.

The spelling of 21640651 in words is "twenty-one million, six hundred forty thousand, six hundred fifty-one".