A026200 a(n) = (s(n) + 2)/3, where s(n) is the n-th number congruent to 1 mod 3 in A026166.

1, 2, 4, 6, 3, 8, 10, 12, 5, 14, 16, 18, 7, 20, 22, 24, 9, 26, 28, 30, 11, 32, 34, 36, 13, 38, 40, 42, 15, 44, 46, 48, 17, 50, 52, 54, 19, 56, 58, 60, 21, 62, 64, 66, 23, 68, 70, 72, 25, 74, 76, 78, 27, 80, 82, 84, 29, 86, 88, 90, 31, 92, 94

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Examples

			Conjectures from _Colin Barker_, Oct 14 2019: (Start)
G.f.: x*(1 + 2*x + 4*x^2 + 6*x^3 + x^4 + 4*x^5 + 2*x^6) / ((1 - x)^2*(1 + x)^2*(1 + x^2)^2).
a(n) = 2*a(n-4) - a(n-8) for n>8.
(End)
		

Links

• Andrew Howroyd, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A026166.

Programs

PARI

\\ here S is A026166 as vector.
S(n)={my(a=vector(n)); a[1]=1; for(i=1, 2*n-1, my(h=(i-1)\2); if(!a[i-h], a[i-h]=i, if(i+h<=n, a[i+h]=i))); a}
{[(k + 2)/3 | k<-S(500), k%3==1]} \\ Andrew Howroyd, Oct 15 2019

Extensions

Title corrected by Sean A. Irvine, Sep 20 2019