Number of the day: 43661

Properties of the number 43661:

43661 is a cyclic number.
43661 is the 4550^th prime.
43661 has 7 antidivisors and 43660 totatives.
43661 has an oblong digit sum 20 in base 10.
Reversing the decimal digits of 43661 results in a semiprime.
43661 = 21831² - 21830² is the difference of 2 nonnegative squares in 1 way.
43661 is the sum of 2 positive triangular numbers.
43661 is the difference of 2 positive pentagonal numbers in 1 way.
43661 = 35² + 206² is the sum of 2 positive squares in 1 way.
43661 = 6² + 19² + 208² is the sum of 3 positive squares.
43661² = 14420² + 41211² is the sum of 2 positive squares in 1 way.
43661² is the sum of 3 positive squares.
43661 is a proper divisor of 1871³⁷ - 1.
43661 = '43' + '661' is the concatenation of 2 prime numbers.
43661 = '4' + '3661' is the concatenation of 2 semiprime numbers.
43661 is an emirp in (at least) the following bases: 5, 17, 19, 25, 27, 30, 35, 37, 49, 51, 56, 59, 61, 62, 63, 68, 73, 76, 86, 91, 97, and 99.

The number 43661 belongs to the following On-Line Encyclopedia of Integer Sequences (OEIS) sequences (among others):

Sequence numbers and descriptions below are taken from OEIS.
A024861: a(n) = s(1)t(n) + s(2)t(n-1) + ... + s(k)t(n-k+1), where k = [ n/2 ], s = (natural numbers), t = (F(2), F(3), F(4), ... ).
A141025: a(n) = (2^(2+n)-(-1)^n)/3 - 2*n.
A176616: Primes of the form x^2 + 7*y^2, where x and y=x+1 are consecutive natural numbers.
A211061: Number of 2 X 2 matrices having all terms in {1,...,n} and determinant >= n.
A222006: Number of forests of rooted plane binary trees (all nodes have outdegree of 0 or 2) with n total nodes.
A230087: Primes such that prime plus its digit sum is a perfect square.
A253394: Number of (n+1)X(5+1) 0..1 arrays with every 2X2 subblock antidiagonal maximum minus diagonal minimum nondecreasing horizontally and diagonal maximum minus antidiagonal minimum nondecreasing vertically
A272747: Number of active (ON,black) cells at stage 2^n-1 of the two-dimensional cellular automaton defined by "Rule 529", based on the 5-celled von Neumann neighborhood.
A285790: Primes equal to a hexagonal number plus 1.
A285812: Primes equal to a centered 9-gonal number plus 1.