|
|
A121229
|
|
Beginning with a(1) = 1 and a(2) = 2, a(n) is not equal to the product of two consecutive (distinct) earlier terms.
|
|
6
|
|
|
1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
MAPLE
|
option remember;
local a, ispr, i;
if n <=2 then
n;
else
for a from procname(n-1)+1 do
ispr := false ;
for i from 1 to n-2 do
if procname(i)*procname(i+1) = a then
ispr := true ;
break;
end if;
end do:
if not ispr then
return a;
end if;
end do:
end if;
|
|
MATHEMATICA
|
a[n_] := a[n] = Module[{k, ispr, i}, If[n <= 2, n, For[k = a[n - 1] + 1, True, k++, ispr = False; For[i = 1, i <= n - 2, i++, If[a[i]*a[i + 1] == k, ispr = True; Break[]]]; If[!ispr, Return[k]]]]];
|
|
PROG
|
(Python)
from itertools import islice
def agen(): # generator of terms
disallowed, prevk, k = {1, 2}, 2, 3; yield from [1, 2]
while True:
while k in disallowed: k += 1
yield k; disallowed.update([k, k*prevk]); prevk = k
|
|
CROSSREFS
|
The complement is A286290, excluding the initial 1.
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|