1621540681 has 2 divisors, whose sum is σ = 1621540682. Its totient is φ = 1621540680.

The previous prime is 1621540667. The next prime is 1621540703. The reversal of 1621540681 is 1860451261.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1357185600 + 264355081 = 36840^2 + 16259^2 .

It is a cyclic number.

It is not a de Polignac number, because 1621540681 - 2⁷ = 1621540553 is a prime.

It is a super-2 number, since 2×1621540681² = 5258788360275887522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1621543681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810770340 + 810770341.

It is an arithmetic number, because the mean of its divisors is an integer number (810770341).

Almost surely, 2^1621540681 is an apocalyptic number.

It is an amenable number.

1621540681 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621540681 is an equidigital number, since it uses as much as digits as its factorization.

1621540681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11520, while the sum is 34.

The square root of 1621540681 is about 40268.3583102167. The cubic root of 1621540681 is about 1174.8324930371.

The spelling of 1621540681 in words is "one billion, six hundred twenty-one million, five hundred forty thousand, six hundred eighty-one".