21215969 has 2 divisors, whose sum is σ = 21215970. Its totient is φ = 21215968.

The previous prime is 21215963. The next prime is 21215977. The reversal of 21215969 is 96951212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10975969 + 10240000 = 3313^2 + 3200^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215969 - 2¹² = 21211873 is a prime.

It is a super-2 number, since 2×21215969² = 900234681217922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21215963) 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, 10607984 + 10607985.

It is an arithmetic number, because the mean of its divisors is an integer number (10607985).

Almost surely, 2^21215969 is an apocalyptic number.

It is an amenable number.

21215969 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215969 is an equidigital number, since it uses as much as digits as its factorization.

21215969 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 35.

The square root of 21215969 is about 4606.0795694386. The cubic root of 21215969 is about 276.8349749275.

The spelling of 21215969 in words is "twenty-one million, two hundred fifteen thousand, nine hundred sixty-nine".