21290813 has 2 divisors, whose sum is σ = 21290814. Its totient is φ = 21290812.

The previous prime is 21290779. The next prime is 21290839. The reversal of 21290813 is 31809212.

It is an a-pointer prime, because the next prime (21290839) can be obtained adding 21290813 to its sum of digits (26).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21132409 + 158404 = 4597^2 + 398^2 .

It is a cyclic number.

It is not a de Polignac number, because 21290813 - 2¹² = 21286717 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21292813) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10645406 + 10645407.

It is an arithmetic number, because the mean of its divisors is an integer number (10645407).

Almost surely, 2^21290813 is an apocalyptic number.

It is an amenable number.

21290813 is a deficient number, since it is larger than the sum of its proper divisors (1).

21290813 is an equidigital number, since it uses as much as digits as its factorization.

21290813 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 21290813 is about 4614.1968965357. The cubic root of 21290813 is about 277.1601249812.

The spelling of 21290813 in words is "twenty-one million, two hundred ninety thousand, eight hundred thirteen".