1,1

Semiprime analogue of A034953 Triangular numbers (A000217) with prime indices.

a(n) = A000217(A001358(n)) = A001358(n)*(A001358(n)+1)/2.

a(1) = semiprime(1)*(semiprime(1)+1)/2 = 4*5/2 = 10.

a(2) = semiprime(2)*(semiprime(2)+1)/2 = 6*7/2 = 21.

a(3) = semiprime(3)*(semiprime(3)+1)/2 = 9*10/2 = 45.

Cf. A000217, A001358, A034953.

Sequence in context: A086225 A014007 A074254 this_sequence A067520 A042309 A048697

Adjacent sequences: A122960 A122961 A122962 this_sequence A122964 A122965 A122966

nonn

Jonathan Vos Post (jvospost3(AT)gmail.com), Oct 26 2006