A353536 a(n) is the cardinality of the set S(n) obtained by the following process: Start with the set S(0) = {i}, where i is the imaginary unit. In step n, the set S(n) is the union of all Gaussian integers obtained by the m*(m+1)/2 sums and the m*(m+1)/2 products formed with the pairs of numbers in the Cartesian product S(n-1) x S(n-1) with m = card(S(n-1)).

1, 2, 6, 34, 458, 41846, 169022181

Offset

0,2

Links

Table of n, a(n) for n=0..6.

Hugo Pfoertner, Illustration of terms a(0)-a(4).

Hugo Pfoertner, Illustration of a(5) = 41846.

Example

S(0) = {i}, a(0) = 1;
S(1) = {-1, 2*i}, a(1) = 2;
S(2) = {-4, -2, 1, -1+2*i, -2*i, 4*i}, a(2) = 6;
S(3) = {-16, -8, -6, -4, -3, -2, -1, 1, 2, 4, 8, 16, -8-4*i, -5+2*i, -4-2*i, -4+4*i, -3-4*i, -3+2*i, -2-2*i, -2+4*i, -1+2*i, -1+6*i, -16*i, -8*i, -4*i, -2*i, 2*i, 4*i, 8*i, 1-2*i, 1+4*i, 2-4*i, 4-8*i, 4+2*i}, a(3) = 34.

Prog

(PARI) a353536(nmax) = {my(v=[I], m=#v); print1(m, ", "); for(n=1, nmax, my(L=m*(m+1), w=vector(L), k=0); for(i=1, #v, for(j=i, #v, w[k++]=v[i]+v[j]; w[k++]=v[i]*v[j])); v=Set(w); m=#v; print1(m, ", "))};
a353536(5)

Crossrefs

Cf. A352969, A353535.

Sequence in context: A118186 A317080 A075272 * A224913 A327038 A228931

Adjacent sequences: A353533 A353534 A353535 * A353537 A353538 A353539

Keyword

nonn,hard,more

Author

Hugo Pfoertner, Apr 26 2022

Status

approved