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A336251
a(1) = 15; for n > 1, a(n)^2 is the smallest square that begins with a(n-1) in base 6.
1
15, 57, 111, 155, 183, 199, 508, 812, 171, 471, 319, 643, 913, 1088, 2909, 11650, 9518, 21074, 31357, 93691, 396693, 55540, 50905, 119374, 182804, 226216, 251647, 265415, 111280, 72055, 142024, 13567, 25160, 34262, 39982, 105795, 172093, 537634
OFFSET
1,1
COMMENTS
The sequence becomes periodic after 491 terms with a period of 10.
The only square in this sequence is 25 and the sequence becomes periodic two terms later.
The maximum value is a(226) = 325880259349618.
LINKS
FORMULA
a(n+1) = ceiling(sqrt(a(n)*6^i)) such that floor(sqrt((a(n)+1)*6^i-1)) > floor(sqrt(a(n)*6^i-1)) where i is a whole number and minimized.
For n > 481, a(n) = a(n+10).
EXAMPLE
The first 10 a(n) alongside the base 6 representations of a(n) and squares of a(n+1):
n a(n) a(n) b6 a(n+1)^2 b6
-- ---- ------- -----------
1 15 23 23013
2 57 133 133013
3 111 303 303121
4 155 415 415013
5 183 503 503201
6 199 531 5310424
7 508 2204 22044304
8 812 3432 343213
9 171 443 4431013
10 471 2103 2103041
PROG
(PARI) lista(nn) = {my(a = 15); for (n=2, nn, print1(a, ", "); my(i=1); while((sqrtint((a+1)*6^i-1) <= sqrtint(a*6^i-1)), i++); a = ceil(sqrt(a*6^i)); ); } \\ Michel Marcus, Jul 15 2020
CROSSREFS
Sequence in context: A140379 A020222 A256867 * A158482 A184223 A084815
KEYWORD
nonn,base
AUTHOR
Sean Lipton, Jul 14 2020
STATUS
approved