21951409 has 2 divisors, whose sum is σ = 21951410. Its totient is φ = 21951408.

The previous prime is 21951389. The next prime is 21951427. The reversal of 21951409 is 90415912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18447025 + 3504384 = 4295^2 + 1872^2 .

It is a cyclic number.

It is not a de Polignac number, because 21951409 - 2⁹ = 21950897 is a prime.

It is a super-3 number, since 3×21951409³ (a number of 23 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (21951469) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10975704 + 10975705.

It is an arithmetic number, because the mean of its divisors is an integer number (10975705).

Almost surely, 2^21951409 is an apocalyptic number.

It is an amenable number.

21951409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21951409 is an equidigital number, since it uses as much as digits as its factorization.

21951409 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21951409 is about 4685.2330785138. The cubic root of 21951409 is about 279.9974872223.

The spelling of 21951409 in words is "twenty-one million, nine hundred fifty-one thousand, four hundred nine".