OFFSET
1,2
COMMENTS
The 2-smooth variant of this sequence, say b, satisfies b(n) = A001045(n+1) for any n > 0.
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10000
Rémy Sigrist, Scatterplot of the first 6500000 terms
Rémy Sigrist, C++ program for A317687
EXAMPLE
The first terms, alongside a(n) + a(n+1), are:
n a(n) a(n) + a(n+1)
-- ---- -------------
1 1 3
2 2 2 * 3
3 4 3^2
4 5 2^3
5 3 3^2
6 6 2^4
7 10 2 * 3^2
8 8 2^3 * 3
9 16 3^3
10 11 2 * 3^2
MATHEMATICA
Nest[Append[#, Block[{k = 2}, While[Nand[FreeQ[#, k], SubsetQ[{2, 3}, FactorInteger[k + #[[-1]] ][[All, 1]]]], k++]; k]] &, {1}, 65] (* Michael De Vlieger, Aug 05 2018 *)
PROG
(C++) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Aug 04 2018
STATUS
approved