21954208621 has 2 divisors, whose sum is σ = 21954208622. Its totient is φ = 21954208620.

The previous prime is 21954208583. The next prime is 21954208643. The reversal of 21954208621 is 12680245912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21922059721 + 32148900 = 148061^2 + 5670^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21954208621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21954208651) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10977104310 + 10977104311.

It is an arithmetic number, because the mean of its divisors is an integer number (10977104311).

Almost surely, 2^21954208621 is an apocalyptic number.

It is an amenable number.

21954208621 is a deficient number, since it is larger than the sum of its proper divisors (1).

21954208621 is an equidigital number, since it uses as much as digits as its factorization.

21954208621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 69120, while the sum is 40.

The spelling of 21954208621 in words is "twenty-one billion, nine hundred fifty-four million, two hundred eight thousand, six hundred twenty-one".