[seqfan] Re: A159559

[K. Brockhaus]

nextcomposite(n)=
{if(n<4, n=4); k=n; while(isprime(k), k++); k}

{z=100; v=vector(z); v[1]=2;
for(n=2, z,
if(isprime(n),
v[n]=nextprime(v[n-1]+1),
v[n]=nextcomposite(v[n-1]+1) ));
print(v)};

[2, 3, 5, 6, 7, 8, 11, 12, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 29, 
30, 32, 33, 37, 38, 39, 40, 42, 44, 47, 48, 53, 54, 55, 56, 57, 58, 59, 
60, 62, 63, 67, 68, 71, 72, 74, 75, 79, 80, 81, 82, 84, 85, 89, 90, 91, 
92, 93, 94, 97, 98, 101, 102, 104, 105, 106, 108, 109, 110, 111, 112, 
113, 114, 127, 128, 129, 130, 132, 133, 137, 138, 140, 141, 149, 150, 
152, 153, 154, 155, 157, 158, 159, 160, 161, 162, 164, 165, 167, 168, 
169, 170]

I think offset 1, a(1) = 2, is natural.

Klaus