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A366921
a(n) is the least prime factor > 3 of 10^n - 1.
2
11, 37, 11, 41, 7, 239, 11, 37, 11, 21649, 7, 53, 11, 31, 11, 2071723, 7, 1111111111111111111, 11, 37, 11, 11111111111111111111111, 7, 41, 11, 37, 11, 3191, 7, 2791, 11, 37, 11, 41, 7, 2028119, 11, 37, 11, 83, 7, 173, 11, 31, 11, 35121409, 7, 239, 11, 37, 11, 107
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OFFSET
2,1
LINKS
Table of n, a(n) for n=2..53.
EXAMPLE
a(2) = 11 because 99 = 3^2 * 11 = 3^
A366922
(2) *
A003020
(2).
a(9) = 37 because 10^9 - 1 = 3^4 * 37 * 333667 = 3^
A366922
(9) * 37 *
A003020
(9).
PROG
(PARI) a366921(n) = factor(10^n-1)[2, 1]
CROSSREFS
Cf.
A002283
,
A003020
,
A102347
,
A366922
.
Sequence in context:
A004637
A191296
A052526
*
A306498
A195201
A233403
Adjacent sequences:
A366918
A366919
A366920
*
A366922
A366923
A366924
KEYWORD
nonn
AUTHOR
Hugo Pfoertner
, Oct 28 2023
STATUS
approved
