21959221 has 2 divisors, whose sum is σ = 21959222. Its totient is φ = 21959220.

The previous prime is 21959213. The next prime is 21959239. The reversal of 21959221 is 12295912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21958596 + 625 = 4686^2 + 25^2 .

It is a cyclic number.

It is not a de Polignac number, because 21959221 - 2³ = 21959213 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21959251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10979610 + 10979611.

It is an arithmetic number, because the mean of its divisors is an integer number (10979611).

Almost surely, 2^21959221 is an apocalyptic number.

It is an amenable number.

21959221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21959221 is an equidigital number, since it uses as much as digits as its factorization.

21959221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 31.

The square root of 21959221 is about 4686.0666875323. The cubic root of 21959221 is about 280.0306981649.

The spelling of 21959221 in words is "twenty-one million, nine hundred fifty-nine thousand, two hundred twenty-one".