21621577 has 2 divisors, whose sum is σ = 21621578. Its totient is φ = 21621576.

The previous prime is 21621557. The next prime is 21621629. The reversal of 21621577 is 77512612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20331081 + 1290496 = 4509^2 + 1136^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21621577 is a prime.

It is not a weakly prime, because it can be changed into another prime (21621527) 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, 10810788 + 10810789.

It is an arithmetic number, because the mean of its divisors is an integer number (10810789).

Almost surely, 2^21621577 is an apocalyptic number.

It is an amenable number.

21621577 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621577 is an equidigital number, since it uses as much as digits as its factorization.

21621577 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5880, while the sum is 31.

The square root of 21621577 is about 4649.9007516290. The cubic root of 21621577 is about 278.5880320839.

The spelling of 21621577 in words is "twenty-one million, six hundred twenty-one thousand, five hundred seventy-seven".