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 A243303 Least number k > 0 such that 2^k contains an n-digit long substring of the infinite string "98765432109876543210987654..." 0
 1, 5, 25, 78, 161, 341, 1076, 16361, 19383, 56047, 132903, 862935, 862935, 4381548 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(n+1) >= a(n) for all n. LINKS EXAMPLE 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. PROG (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 CROSSREFS Cf. A243150. Sequence in context: A056374 A301912 A171272 * A238449 A062989 A122679 Adjacent sequences:  A243300 A243301 A243302 * A243304 A243305 A243306 KEYWORD nonn,base,hard,more AUTHOR Derek Orr, Jun 04 2014 EXTENSIONS a(10)-a(13) from Hiroaki Yamanouchi, Sep 26 2014 a(14) from Chai Wah Wu, May 29 2020 STATUS approved

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Last modified August 3 10:49 EDT 2020. Contains 336198 sequences. (Running on oeis4.)