21028517 has 2 divisors, whose sum is σ = 21028518. Its totient is φ = 21028516.

The previous prime is 21028493. The next prime is 21028549. The reversal of 21028517 is 71582012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20784481 + 244036 = 4559^2 + 494^2 .

It is a cyclic number.

It is not a de Polignac number, because 21028517 - 2²⁰ = 19979941 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21028597) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10514258 + 10514259.

It is an arithmetic number, because the mean of its divisors is an integer number (10514259).

Almost surely, 2^21028517 is an apocalyptic number.

It is an amenable number.

21028517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21028517 is an equidigital number, since it uses as much as digits as its factorization.

21028517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21028517 is about 4585.6860991568. The cubic root of 21028517 is about 276.0172440742.

The spelling of 21028517 in words is "twenty-one million, twenty-eight thousand, five hundred seventeen".