A080905 Sequence of run lengths in first differences of A080900.

4, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2, 1, 4, 1, 4, 1, 2, 1, 1, 1, 2

Offset: 1

Author

N. J. A. Sloane, Apr 01 2003

Keywords

• nonn

Comments

Even after 400000 terms there is no clear pattern here.

Examples

			A080900 begins 1, 6, 11, 16, 21, 19, 24, 29, 34, 39, 37, 42, 47, 52, 57, 55, 60, 65, ..., the differences are 5, 5, 5, 5, -2, 5, 5, 5, 5, -2, ... with runs of lengths 4, 1, 4, 1, ...
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..102526

Crossrefs

Cf. A080900, A080922, A080927.

Programs

PARI

up_to = 20000;
A080905list(up_to_n) = { my(xs=Map(), v, d, ds=vector(up_to_n)); mapput(xs,1,1); v = 1; for(n=2,1+up_to_n, v += (d=if(mapisdefined(xs,n), -2, +5)); mapput(xs,v,n); ds[n-1] = d); my(runlens=List([]), rl=1); for(i=2,#ds,if(ds[i]==ds[i-1],rl++, listput(runlens,rl);rl=1)); Vec(runlens); };
v080905 = A080905list(up_to);
A080905(n) = v080905[n]; \\ Antti Karttunen, Feb 24 2020