This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A119707 #5 Oct 31 2013 12:17:39 %S A119707 0,1,1,1,3,2,4,3,4,4,5,4,6,5,6,6,7,6,8,7,8,8,9,8,9,9,9,9,10,9,11,10, %T A119707 11,11,11,11,12,11,12,12,13,12,14,13,14,14,15,14,15,15,15,15,16,15,16, %U A119707 16,16,16,17,16,18,17,18,18,18,18,19,18,19,19,20,19,21,20,21,21,21,21,22 %N A119707 Number of distinct primes appearing in all partitions of n into prime parts. %F A119707 When n = odd and >=5 then a(n) = pi(n) = A000720(n). When n = even and >=4 then a(n) = pi(n-2) = A000720(n-2) %e A119707 There is only 1 distinct prime number involved in the partitions of 4, namely 2 (in 2+2 = 4). The partition 3+1 does not count, as 1 is not a prime. So a(4)= 1. %e A119707 There are 3 distinct primes involved in the partitions of 5 = 2+3, so a(5) = 3. %t A119707 f[n_] := If[OddQ@n, If[n == 3, 1, PrimePi@n], If[n == 2, 1, PrimePi[n - 2]]]; Array[f, 80] (* _Robert G. Wilson v_ *) %Y A119707 Cf. A000720. %K A119707 nonn %O A119707 1,5 %A A119707 _Anton Joha_, Jun 10 2006 %E A119707 Edited and extended by _Robert G. Wilson v_, Jun 15 2006