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A116136
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Numbers k such that k concatenated with k-3 gives the product of two numbers which differ by 4.
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11
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9, 99, 183, 328, 528, 715, 999, 6099, 9999, 13224, 40495, 99999, 106755, 453288, 999999, 2066115, 2975208, 9999999, 22145328, 28027683, 99999999, 110213248, 110667555, 147928995, 178838403, 226123528, 275074575, 333052608, 378698224, 445332888, 446245635, 518348515
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OFFSET
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1,1
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COMMENTS
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Also numbers k such that k concatenated with itself gives the product of two numbers which differ by 2.
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LINKS
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EXAMPLE
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8315420899//8315420896 = 9118892968 * 9118892972, where // denotes concatenation.
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PROG
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(Python)
from itertools import count, islice
from sympy import sqrt_mod
def A116136_gen(): # generator of terms
for j in count(0):
b = 10**j
a = b*10+1
for k in sorted(sqrt_mod(1, a, all_roots=True)):
if a*(b+3) <= k**2-1 < a*(a+2):
yield (k**2-1)//a
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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