A116254 k times k+4 gives the concatenation of two numbers m and m-5.

89, 9077, 9899, 733672, 998999, 88225293, 99989999, 8900869206, 9296908810, 9604060395, 9999899999, 326666333265, 673333666732, 700730927006, 972603739725, 999998999999, 34519562953735, 39737862788836, 49917309624954, 50082690375043, 60262137211161, 65480437046262

Offset: 1

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn
• base

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..3000

Crossrefs

Cf. A054214, A116248, A116253, A116255, A116260.

Programs

Python

from itertools import count, islice
from sympy import sqrt_mod
def A116254_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)):
            m = (k**2+1)//a
            if a*(b+4) <= k**2+1 < a*(a+3):
                yield k-2
A116254_list = list(islice(A116254_gen(),40)) # Chai Wah Wu, Feb 19 2024

Extensions

a(19)-a(22) from Chai Wah Wu, Feb 19 2024