21801517 has 2 divisors, whose sum is σ = 21801518. Its totient is φ = 21801516.

The previous prime is 21801511. The next prime is 21801553. The reversal of 21801517 is 71510812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13995081 + 7806436 = 3741^2 + 2794^2 .

It is a cyclic number.

It is not a de Polignac number, because 21801517 - 2¹⁵ = 21768749 is a prime.

It is a super-2 number, since 2×21801517² = 950612287002578, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21801491 and 21801500.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21801511) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10900758 + 10900759.

It is an arithmetic number, because the mean of its divisors is an integer number (10900759).

Almost surely, 2^21801517 is an apocalyptic number.

It is an amenable number.

21801517 is a deficient number, since it is larger than the sum of its proper divisors (1).

21801517 is an equidigital number, since it uses as much as digits as its factorization.

21801517 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 25.

The square root of 21801517 is about 4669.2094619968. The cubic root of 21801517 is about 279.3587237505.

The spelling of 21801517 in words is "twenty-one million, eight hundred one thousand, five hundred seventeen".