21406993409 has 2 divisors, whose sum is σ = 21406993410. Its totient is φ = 21406993408.

The previous prime is 21406993373. The next prime is 21406993429. The reversal of 21406993409 is 90439960412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19405325809 + 2001667600 = 139303^2 + 44740^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406993409 - 2¹² = 21406989313 is a prime.

It is not a weakly prime, because it can be changed into another prime (21406993429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703496704 + 10703496705.

It is an arithmetic number, because the mean of its divisors is an integer number (10703496705).

Almost surely, 2^21406993409 is an apocalyptic number.

It is an amenable number.

21406993409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406993409 is an equidigital number, since it uses as much as digits as its factorization.

21406993409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 419904, while the sum is 47.

The spelling of 21406993409 in words is "twenty-one billion, four hundred six million, nine hundred ninety-three thousand, four hundred nine".