21951389 has 2 divisors, whose sum is σ = 21951390. Its totient is φ = 21951388.

The previous prime is 21951383. The next prime is 21951409. The reversal of 21951389 is 98315912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21548164 + 403225 = 4642^2 + 635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21951389 - 2¹² = 21947293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21951383) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10975694 + 10975695.

It is an arithmetic number, because the mean of its divisors is an integer number (10975695).

Almost surely, 2^21951389 is an apocalyptic number.

It is an amenable number.

21951389 is a deficient number, since it is larger than the sum of its proper divisors (1).

21951389 is an equidigital number, since it uses as much as digits as its factorization.

21951389 is an evil number, because the sum of its binary digits is even.

The product of its digits is 19440, while the sum is 38.

The square root of 21951389 is about 4685.2309441478. The cubic root of 21951389 is about 279.9974021868.

The spelling of 21951389 in words is "twenty-one million, nine hundred fifty-one thousand, three hundred eighty-nine".