A116283 k times k+7 gives the concatenation of two numbers m and m-1.

7, 30, 64, 42753, 57241, 75423, 425072, 574922, 979528, 4301393, 5698601, 7028666, 4925000747, 5074999247, 7748266574, 8511881484, 8814851184, 7059602159672, 7106167933828, 7439286611621, 7485852385777

Offset: 1

Author

Giovanni Resta, Feb 06 2006

Keywords

• nonn
• base

Crossrefs

Cf. A001704, A028563.

Cf. A116152, A116269, A116282, A116284, A116291.

Programs

Python

def ok(n):
    s = str(n*(n+7)); h = (len(s)+1)//2; return int(s[:h])-1 == int(s[h:])
print(list(filter(ok, range(2, 10**6)))) # Michael S. Branicky, Jul 30 2021