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A116288

Numbers k such that k*(k+4) gives the concatenation of a number m with itself.

7, 97, 451, 546, 689, 854, 997, 4380, 5617, 9997, 72728, 99997, 346531, 653466, 999997, 9090906, 9999997, 94117644, 99999997, 334665331, 336032385, 378253326, 390977440, 439928489, 483516484, 516483513, 560071508

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OFFSET

1,1

COMMENTS

Contains 10^m - 3 hence the sequence is infinite. - David A. Corneth, Feb 20 2024

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..10000

PROG

(Python)

from itertools import count, islice

from sympy import sqrt_mod

def A116288_gen(): # generator of terms

for j in count(0):

b = 10**j

a = b*10+1

for k in sorted(sqrt_mod(4, a, all_roots=True)):

if a*b <= k**2-4 < a*(a-1):

yield k-2

A116288_list = list(islice(A116288_gen(), 40)) # Chai Wah Wu, Feb 20 2024

CROSSREFS

Cf. A116125, A116275, A116287, A116289, A116297.

Sequence in context: A116125 A142315 A359637 * A219088 A116261 A289851

Adjacent sequences: A116285 A116286 A116287 * A116289 A116290 A116291

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, Feb 06 2006

STATUS

approved

URL: https://oeis.org/A116288

⇱ A116288 - OEIS