21930421 has 2 divisors, whose sum is σ = 21930422. Its totient is φ = 21930420.

The previous prime is 21930413. The next prime is 21930443. The reversal of 21930421 is 12403912.

It is an a-pointer prime, because the next prime (21930443) can be obtained adding 21930421 to its sum of digits (22).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16313521 + 5616900 = 4039^2 + 2370^2 .

It is a cyclic number.

It is not a de Polignac number, because 21930421 - 2³ = 21930413 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21930392 and 21930401.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21930721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965210 + 10965211.

It is an arithmetic number, because the mean of its divisors is an integer number (10965211).

Almost surely, 2^21930421 is an apocalyptic number.

It is an amenable number.

21930421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21930421 is an equidigital number, since it uses as much as digits as its factorization.

21930421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21930421 is about 4682.9927396911. The cubic root of 21930421 is about 279.9082224718.

The spelling of 21930421 in words is "twenty-one million, nine hundred thirty thousand, four hundred twenty-one".