21225661 has 2 divisors, whose sum is σ = 21225662. Its totient is φ = 21225660.

The previous prime is 21225653. The next prime is 21225671. The reversal of 21225661 is 16652212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20985561 + 240100 = 4581^2 + 490^2 .

It is a cyclic number.

It is not a de Polignac number, because 21225661 - 2³ = 21225653 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21225671) 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, 10612830 + 10612831.

It is an arithmetic number, because the mean of its divisors is an integer number (10612831).

Almost surely, 2^21225661 is an apocalyptic number.

It is an amenable number.

21225661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21225661 is an equidigital number, since it uses as much as digits as its factorization.

21225661 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21225661 is about 4607.1315370847. The cubic root of 21225661 is about 276.8771236209.

Adding to 21225661 its reverse (16652212), we get a palindrome (37877873).

The spelling of 21225661 in words is "twenty-one million, two hundred twenty-five thousand, six hundred sixty-one".