A081843 a(1)=0, a(n)=a(n-1)+5 if n is already in th sequence, a(n)=a(n-1)+4 otherwise.

0, 4, 8, 13, 17, 21, 25, 30, 34, 38, 42, 46, 51, 55, 59, 63, 68, 72, 76, 80, 85, 89, 93, 97, 102, 106, 110, 114, 118, 123, 127, 131, 135, 140, 144, 148, 152, 157, 161, 165, 169, 174, 178, 182, 186, 191, 195, 199, 203, 207, 212, 216, 220, 224, 229, 233, 237, 241