Sequences

Well-order the rational numbers; take numerators.

Well-order the rational numbers; take denominators.

Erroneous version of A001679.

Numerators of coefficients of Eisenstein series E_12(q) (or E_6(q) or E_24(q)).

a(n) = prime(n)*prime(n+1) - prime(n) - prime(n+1).

a(n) = prime(n)*prime(n+1) - prime(n).

a(n) = prime(n)*prime(n+1) - prime(n+1).

a(n) = 2*prime(n) - 2.

a(n) = prime(n) * Product_{k=0..n-2} prime(n-k) mod prime(n-k-1).

Numbers n such that n = pi(n) + phi(n), where pi = A000720, phi = A000010.

Numbers n such that phi(n) = pi(n), i.e., A000010(n) = A000720(n).

Numbers n such that sigma(n) - n = {number of primes <= n}.

Numbers that are not the sum of consecutive composite numbers.

Primes which are not the sum of consecutive composite numbers.

Numbers k such that |s(k) - k| = number of primes <= k, where s(k) is sigma(k) - k.

Numbers k such that us(k) = primepi(k), where us(k) is the sum of the aliquot unitary divisors of k (A034460), and primepi(k) is the number of primes <= k (A000720).

Numbers k such that 2047*2^k+1 is prime.

Longest cycle when squaring modulo n-th prime.

Number of cycles when squaring modulo n-th prime.

Number of different cycle lengths when squaring modulo n-th prime.

Incorrect version of A107357.

a(n) = 10^n*(10^n-1)/2.

Smallest number that is palindromic (with at least 2 digits) in n bases.

Functional digraphs with 1 node not in the image.

Number of ways of placing 2n points on n X n grid so no 3 are in a line (solutions with no symmetry).

Number of ways of placing 2n points on n X n grid so no 3 are in a line (solutions with symmetry about one main diagonal).

Number of ways of placing 2n points on n X n grid so no 3 are in a line (solutions with 180 deg rotational symmetry).

Number of ways of placing 2n points on n X n grid so no 3 are in a line (solutions with symmetry about both main diagonals).

Number of ways of placing 4n points on 2n X 2n grid so no 3 are in a line (solutions with either 90-degree rotational symmetry or full symmetry).

Theta series of lattice A_2 tensor D12+ (dimension 24, min norm 4).

Theta series of lattice A_2 tensor E_7^2+ (dimension 28, min norm 4).

Summarize the previous term!, starting with 8899.

Number of consonants in n (in French).

Number of vowels in n (in French).

Number of consonants in the American English name of n.

Number of vowels in the American English name of n.

Numbers k such that tau(sigma(k)) = tau(k) where tau(k) is the number of divisors of k and sigma(k) their sum.

Number of divisors of (sigma(n)-n) = number of divisors of n.

Number of consonants in n (in German).

Number of vowels in n (in German).

Differences between consecutive primes (A001223) but with repeats omitted.

Number of lines in Pratt certificate for n-th prime.

Number of terms by which A001223 lags behind A037201.

Numbers that occur in runs of length 1 in A037203.

a(n) = (n+1)^n - 1.

Duplicate of A065530.

Smallest natural number k such that periodic part of 1/k is n, or 0 if no such k exists.

Numbers k such that q^2 < p, where p=nextprime(k), q=nextprime(square root of k).

Primes p such that nextprime(p) - p = ( number of divisors of (nextprime(p)+p)/2 )-1.

Numbers k such that p-k=p#-k#, where p=nextprime(k), k#=nextprime(square root of k), p#=nextprime(square root of p).