|
|
A138621
|
|
a(1)=2. For n >=2, a(n) = p(n) *(floor(a(n-1)/p(n)) +2), where p(n) is the n-th prime.
|
|
1
|
|
|
2, 6, 15, 28, 44, 65, 85, 114, 138, 174, 217, 259, 328, 387, 470, 530, 590, 671, 804, 923, 1022, 1106, 1245, 1335, 1455, 1616, 1751, 1926, 2071, 2260, 2413, 2620, 2877, 3058, 3278, 3473, 3768, 4075, 4342, 4671, 5012, 5249, 5539, 5790, 6107, 6368, 6752, 7136
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
a(n) is the next-to-least multiple of the n-th prime that is > a(n-1).
If we instead had the sequence where a(1)=2 and where a(n) is the least multiple of the n-th prime that is > a(n-1), then a(n) would equal the n-th prime for all positive integers n.
|
|
LINKS
|
|
|
MAPLE
|
A138621 := proc(n) option remember ; local a ; if n = 1 then RETURN(2) ; fi ; p := ithprime(n) ; p*(floor(A138621(n-1)/p)+2) ; end: seq(A138621(n), n=1..80) ; # R. J. Mathar, May 20 2008
|
|
MATHEMATICA
|
a = {2}; Do[AppendTo[a, Prime[n]*(Floor[a[[ -1]]/Prime[n]] + 2)], {n, 2, 60}]; a (* Stefan Steinerberger, May 18 2008 *)
nxt[{n_, a_}]:={n+1, Prime[n+1](Floor[a/Prime[n+1]]+2)}; Transpose[NestList[nxt, {1, 2}, 50]][[2]] (* Harvey P. Dale, Mar 18 2013 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|