letters in n, cardinals vs ordinals

[N. J. A. Sloane]

Is this interesting to anyone but me?

1, 1, 1, 1, 1, 1, 3, 5, 5, 6, 7, 7, 13, 17, 18, 20, 30, 37, 47

Semiprimonacci numbers:
a(n)=a(n-4)+a(n-6)+a(n-9)+a(n-10)+a(n-14)+...+a(n-sp(k))+... until n >
sp(k), where sp(k) is the k-th semprime = A001358(k);
a(1)=a(2)=a(3)=1.