1621653961 has 2 divisors, whose sum is σ = 1621653962. Its totient is φ = 1621653960.

The previous prime is 1621653947. The next prime is 1621653991. The reversal of 1621653961 is 1693561261.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1581255225 + 40398736 = 39765^2 + 6356^2 .

It is a cyclic number.

It is not a de Polignac number, because 1621653961 - 2⁷ = 1621653833 is a prime.

It is not a weakly prime, because it can be changed into another prime (1621653941) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 810826980 + 810826981.

It is an arithmetic number, because the mean of its divisors is an integer number (810826981).

Almost surely, 2^1621653961 is an apocalyptic number.

It is an amenable number.

1621653961 is a deficient number, since it is larger than the sum of its proper divisors (1).

1621653961 is an equidigital number, since it uses as much as digits as its factorization.

1621653961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 58320, while the sum is 40.

The square root of 1621653961 is about 40269.7648490775. The cubic root of 1621653961 is about 1174.8598501318.

The spelling of 1621653961 in words is "one billion, six hundred twenty-one million, six hundred fifty-three thousand, nine hundred sixty-one".