OFFSET
1,2
COMMENTS
This is an increasing sequence (but not necessarily strictly increasing).
EXAMPLE
7 is the smallest exponent such that 2^7 contains two consecutive increasing digits (2^7 = 128).
28 is the smallest exponent such that 2^28 ( = 268435456) contains three consecutive increasing digits (456).
a(6) = 992 from 2^992 =
418558049682135672245478534789063207250548754572474065407714995457168379_345\
678_17284890561672488119458109166910841919797858872862722356017328064756\
15116630782786940537040715228680107267602488727296075852403533779290461\
69580757764357779904060393635270100437362409630553424235540298930640110\
82834640896 - N. J. A. Sloane, Aug 12 2018
MATHEMATICA
a[1]=0; a[n_] := Block[{k = 4, p = 16}, While[Max[ Length /@ Select[ Split@ Differences@ IntegerDigits@p, First@# == 1 &]] < n-1, k++; p *= 2]; k]; a/@ Range[7] (* Giovanni Resta, Feb 26 2014 *)
PROG
(Python)
def Str(x):
..for n in range(10**5):
....count = 0
....i = 0
....if len(str(2**n)) == x and x == 1:
......return n
....while i < len(str(2**n))-1:
......if int(str(2**n)[i]) == int(str(2**n)[i+1])-1:
........count += 1
........i += 1
......else:
........if count == x-1:
..........return n
........else:
..........count = 0
..........i += 1
....if count == x-1:
......return n
x = 1
while x < 50:
..print(Str(x))
..x += 1
CROSSREFS
KEYWORD
nonn,base,fini,full
AUTHOR
Derek Orr, Feb 26 2014
EXTENSIONS
a(8)-a(10) from Giovanni Resta, Feb 26 2014
Definition and examples corrected ("integers" changed to "digits") by N. J. A. Sloane, Aug 12 2018
STATUS
approved