|
|
A330293
|
|
a(1) = 1, a(2) = 2; for n > 2, a(n) = the smallest prime divisor of the number formed by the concatenation of a(1) to a(n-1) that has not previously appeared in the sequence.
|
|
2
|
|
|
1, 2, 3, 41, 7, 653, 331, 2536483, 191, 176081, 18307, 2143406938831, 101, 73, 3541, 439, 5665417, 37, 17302849, 86113, 11, 878390431, 2969, 1385625388248048145493629820571541645230648738185397486740279040908468652182116663161996667, 59, 30956837, 181, 151, 159833, 1629097816565791058167, 293, 2063, 3251, 31219483, 13
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
The next term a(36) requires the factorization of a composite 246 digit number 18604...12467.
|
|
LINKS
|
|
|
EXAMPLE
|
a(3) = 3 as the concatenation of a(1) and a(2) = '12' and 3 is the smallest prime divisor of 12 that has not appeared in the sequence.
a(4) = 41 as the concatenation of a(1)..a(3) is '123' and 41 is the smallest prime divisor of 123 which has not appeared in the sequence. Note that 3 also divides 123 but a(3) = 3.
a(6) = 653 as the concatenation of a(1)..a(5) is '123417' and 653 is the smallest prime divisor of 123417 has not appeared in the sequence. Note that 9 also divides 123417 and has not appeared but only prime divisors are considered.
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|