A243303 Least number k > 0 such that 2^k contains an n-digit long substring of the infinite string "98765432109876543210987654...".
1, 5, 25, 78, 161, 341, 1076, 16361, 19383, 56047, 132903, 862935, 862935, 4381548
Offset: 1
Examples
2^25 = 33554432 contains a 3-digit substring of "98765432109876543210987654..." (in this case, "432"). Since 25 is the lower power to have this property, a(3) = 25.
Crossrefs
Cf. A243150.
Programs
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Python
def Rev(n): rev = '' for i in str(n): rev = i + rev return rev def a(n): lst = [] for b in range(1,10**n): if len(str(2**b)) >= n: lst.append(b) break for k in range(lst[0],50000): for i in range(10): s = '' s += str(i) for j in range(i+1,i+n): dig = j%10 s+=str(dig) if str(2**k).find(Rev(s)) > -1: return k n = 1 while n < 100: print(a(n),end=', ') n += 1
Extensions
a(10)-a(13) from Hiroaki Yamanouchi, Sep 26 2014
a(14) from Chai Wah Wu, May 29 2020
Comments