A178901 a(1)=2; for n > 1, a(n) is the largest number <= 2*a(n-1) divisible by n.

2, 4, 6, 12, 20, 36, 70, 136, 270, 540, 1078, 2148, 4290, 8568, 17130, 34256, 68510, 137016, 274018, 548020, 1096032, 2192058, 4384099, 8768184, 17536350, 35072700, 70145379, 140290752, 280581496, 561162990, 1122325953, 2244651904

Offset

1,1

Comments

The definition "a(1)=1; for n > 1, a(n) is the largest number <= 2*a(n-1) divisible by n" produces the natural numbers 1,2,3,4,5,... (A000027).

Links

Table of n, a(n) for n=1..32.

Example

2*36=72. But 72 is not a multiple of 7, so we must look for the largest multiple of 7 <= 72, and this is 70.

Maple

A178901 := proc(n) option remember; if n =1 then 2; else for a from 2*procname(n-1) by -1 do if a mod n = 0 then return a; end if; end do: end if; end proc: seq(A178901(n), n=1..30) ; # R. J. Mathar, Jun 26 2010

Prog

(PARI) lista(nn) = {my(va = vector(nn)); va[1] = 2;  for (n=2, nn, va[n] = n*(2*va[n-1]\n); ); va; } \\ Michel Marcus, Dec 18 2020

Crossrefs

Cf. A000027.

Sequence in context: A294429 A107383 A078025 * A164146 A370582 A279245

Adjacent sequences: A178898 A178899 A178900 * A178902 A178903 A178904

Keyword

nonn

Author

J. Lowell, Jun 21 2010

Extensions

a(8)-a(32) from Robert G. Wilson v and John W. Layman, Jun 28 2010

Status

approved