OFFSET
1,1
COMMENTS
a(n)+1 is divisible by 25 because the string 4,4 must be at the lower end of the base-5 representation. - Joerg Arndt, Feb 13 2012
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
EXAMPLE
49 is in the sequence because its base-5 representation, 144, includes 44 as a substring, but the base-5 representation of 50, 200, does not.
599 is not in the sequence because, although it is 4344 in base 5, 600 is 4400 in base 5.
MATHEMATICA
f[n_]:= Length[StringPosition[ToString[FromDigits[IntegerDigits[n, 5]]], "44", 1]]; Select[Table[n, {n, 2000}], f[#]>0&&f[#+1] == 0&] (* Vincenzo Librandi, Feb 12 2012 *)
SequencePosition[Table[If[SequenceCount[IntegerDigits[n, 5], {4, 4}]>0, 1, 0], {n, 1200}], {1, 0}][[All, 1]] (* Harvey P. Dale, Aug 20 2021 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
STATUS
approved