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A116260 n times n+4 gives the concatenation of two numbers m and m-4. 8
9, 99, 999, 9999, 99999, 999999, 9999999, 99999999, 999999999, 9999999999, 36363636362, 45454545453, 54545454544, 63636363635, 72727272726, 81818181817, 90909090908, 99999999999, 999999999999, 9999999999999 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
10^d-1 for d>0 are terms. - Chai Wah Wu, Feb 19 2024
EXAMPLE
99999999 * 100000003 = 100000001//99999997, where // denotes concatenation.
PROG
(Python)
from itertools import count, islice
from sympy import sqrt_mod
def A116260_gen(): # generator of terms
for j in count(0):
b = 10**j
a = b*10+1
for k in sorted(sqrt_mod(0, a, all_roots=True))+[a]:
if a*(b+4) <= k**2 < a*(a+3):
yield k-2
A116260_list = list(islice(A116260_gen(), 20)) # Chai Wah Wu, Feb 19 2024
CROSSREFS
Sequence in context: A261512 A242809 A108908 * A103456 A002283 A155157
KEYWORD
nonn,base
AUTHOR
Giovanni Resta, Feb 06 2006
STATUS
approved

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Last modified May 17 19:53 EDT 2024. Contains 372607 sequences. (Running on oeis4.)