20606

Appears in sequences

• a(n) = s(1)t(n) + s(2)t(n-1) + ... + s(k)t(n+1-k), where k = [ (n+1)/2 ], s = (composite numbers), t = (primes).at n=31A024604
• Numbers n such that in n^3 the parity of digits alternates.at n=26A030159
• Expansion of (1-x)/(1-x-2x^2+x^4).at n=17A052969
• Numbers n such that phi((prime(n)+1)/2)=sigma(n).at n=35A068473
• Semiprimes of the form 2*(m^2 + m + 1) (implying that m^2 + m + 1 is a prime).at n=32A107317
• The (1,4)-entry in the matrix M^n, where M is the 4 X 4 matrix {{0, -1, -1, 1}, {1, -1, 0, 0}, {0, 1, 1, 0}, {0, 0, 1, 1 }}.at n=36A122789
• Number of nX4 0..2 arrays with exactly floor(nX4/2) elements unequal to at least one horizontal, vertical or antidiagonal neighbor, with new values introduced in row major 0..2 order.at n=5A222669
• Number of nX6 0..2 arrays with exactly floor(nX6/2) elements unequal to at least one horizontal, vertical or antidiagonal neighbor, with new values introduced in row major 0..2 order.at n=3A222671
• T(n,k)=Number of nXk 0..2 arrays with exactly floor(nXk/2) elements unequal to at least one horizontal, vertical or antidiagonal neighbor, with new values introduced in row major 0..2 order.at n=39A222673
• T(n,k)=Number of nXk 0..2 arrays with exactly floor(nXk/2) elements unequal to at least one horizontal, vertical or antidiagonal neighbor, with new values introduced in row major 0..2 order.at n=41A222673
• Numbers k such that sigma(k + sigma(k)) = sigma((k+1) + sigma(k+1)).at n=7A246915
• G.f.: Sum_{k>=0} x^(k^2) * Product_{j=1..k} 1/(1 - x^j)^3.at n=24A376709