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A365994
The n-th term of the sequence is the last term of n's trajectory under the "multiply with zero" rules explained in A365993.
2
101, 3981053, 103, 1196913103, 4185108867, 2053, 107, 13093, 109, 50821, 1319023, 206, 1013, 2309, 1970359, 1160555267, 1435393103, 5147059, 1019, 24786109, 307, 1265393034541, 11093, 1104119, 505, 11409, 309, 44661214906829, 191077, 1210977611, 1031, 18107519, 1033, 33269991281067, 170767
OFFSET
1,1
COMMENTS
It is conjectured that all trajectories will stop quite rapidly, mostly because the probability for 0 to appear in a divisor of a(n) increases with the size of a(n).
LINKS
Eric Angelini, Multiply with zero, personal blog "Cinquante signes" Sept. 2023.
EXAMPLE
Trajectories of n for n = 1 to 40.
A "stop" means that the next term will contain two or more zeros.
n = 1 --> 1, 101, stop
n = 2 --> 2, 102, 1706, 20853, 210993, 3981053, stop
n = 3 --> 3, 103, stop
n = 4 --> 4, 104, 1308, 20654, 230898, 2654087, 35907393, 1196913103, stop
n = 5 --> 5, 105, 1507, 110137, 2410457, 34435107, 371092817, 4185108867, stop
n = 6 --> 6, 106, 2053, stop
n = 7 --> 7, 107, stop
n = 8 --> 8, 108, 1209, 13093, stop
n = 9 --> 9, 109, stop
n = 10 --> 10, 205, 4105, 50821, stop
n = 11 --> 11, 1011, 30337, 1319023, stop
n = 12 --> 12, 206, stop
n = 13 --> 13, 1013, stop
n = 14 --> 14, 207, 2309, stop
n = 15 --> 15, 305, 5061, 70723, 1970359, stop
n = 16 --> 16, 208, 2608, 32608, 408152, 6260652, 64410972, 1160555267, stop
n = 17 --> 17, 1017, 11309, 263043, 2657099, 43061793, 1435393103, stop
n = 18 --> 18, 209, 11019, 303673, 5147059, stop
n = 19 --> 19, 1019, stop
n = 20 --> 20, 405, 4509, 167027, 2230749, 24786109, stop
n = 21 --> 21, 307, stop
n = 22 --> 22, 1022, 14073, 304691, 17017923, 305672641, 3469610881, 43707939613, 1265393034541, stop
n = 23 --> 23, 1023, 11093, stop
n = 24 --> 24, 308, 4077, 45309, 1104119, stop
n = 25 --> 25, 505, stop
n = 26 --> 26, 1026, 11409, stop
n = 27 --> 27, 309, stop
n = 28 --> 28, 407, 11037, 130849, 1707697, 17770961, 1301366997, 14459633309, 149743096563, 3049914365521, 44661214906829, stop
n = 29 --> 29, 1029, 14707, 191077, stop
n = 30 --> 30, 506, 11046, 140789, 11012799, 118290931, 1210977611, stop
n = 31 --> 31, 1031, stop
n = 32 --> 32, 408, 5108, 127704, 1360939, 18107519, stop
n = 33 --> 33, 1033, stop
n = 34 --> 34, 1034, 11094, 129086, 1590817, 21075277, 253919083, 15701617319, 199307878383, 2229089415827, 33269991281067, stop
n = 35 --> 35, 507, 13039, 170767, stop
n = 36 --> 36, 409, stop
n = 37 --> 37, 1037, 17061, 305687, stop
n = 38 --> 38, 1038, 17306, 208653, 3069551, stop
n = 39 --> 39, 1039, stop
n = 40 --> 40, 508, 12704, 158808, 1985108, 20992554, 306997518, 5116625306, 13032065196793281, stop
etc.
MATHEMATICA
Table[Last@Most@NestWhileList[(d=Divisors@#;
Min[Select[FromDigits@Flatten[IntegerDigits/@Riffle[#, 0]]&/@Table[{d[[k]], d[[Length@d-k+1]]}, {k, Length@d}], Count[IntegerDigits@#, 0]<2&]])&, n, IntegerQ], {n, 40}]
PROG
(Python)
from sympy import divisors
def a(n):
k = n
while True:
s = set()
for d in divisors(k, generator=True):
v, w = str(d), str(k//d)
if "0" not in v and "0" not in w:
s.add(int(v + "0" + w))
if len(s) == 0: return k
k = min(s)
print([a(n) for n in range(1, 41)]) # Michael S. Branicky, Sep 26 2023
CROSSREFS
Sequence in context: A138120 A266609 A082521 * A262645 A138826 A292686
KEYWORD
base,nonn
AUTHOR
STATUS
approved