90205721 has 2 divisors, whose sum is σ = 90205722. Its totient is φ = 90205720.

The previous prime is 90205697. The next prime is 90205729. The reversal of 90205721 is 12750209.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80371225 + 9834496 = 8965^2 + 3136^2 .

It is an emirp because it is prime and its reverse (12750209) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 90205721 - 2⁶ = 90205657 is a prime.

It is a super-2 number, since 2×90205721² = 16274144202259682, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (90205729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45102860 + 45102861.

It is an arithmetic number, because the mean of its divisors is an integer number (45102861).

Almost surely, 2^90205721 is an apocalyptic number.

It is an amenable number.

90205721 is a deficient number, since it is larger than the sum of its proper divisors (1).

90205721 is an equidigital number, since it uses as much as digits as its factorization.

90205721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1260, while the sum is 26.

The square root of 90205721 is about 9497.6692403979. The cubic root of 90205721 is about 448.4816663294.

It can be divided in two parts, 9020 and 5721, that added together give a palindrome (14741).

The spelling of 90205721 in words is "ninety million, two hundred five thousand, seven hundred twenty-one".