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A262958 Numbers whose base-b expansions, for both b=3 and b=4, include no digits other than 1 and b-1. 4
1, 5, 7, 13, 23, 53, 125, 215, 373, 1367, 1373, 1375, 3551, 4093, 5471, 5495, 5503, 30581, 30589, 32765, 32767, 56821, 56831, 89557, 96119, 96215, 96223, 97655, 98135, 98141, 98143, 98167, 98293, 98303, 351743, 352093, 521599, 521693, 521717, 521719, 524119, 524149, 875893, 875903, 884725, 884735 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

1, 7 and 32767 also share this property in base 2; their binary expansions consist only of a sequence of 1s.

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..10000

EXAMPLE

53 is 1222 in base 3 and 311 in base 4; it only uses the digit 1 or the largest digit in the two bases and is therefore a term.

Similarly 215 is 21222 in base 3 and 3113 in base 4 so it is also a term.

MATHEMATICA

Select[Range@ 1000000, Last@ DigitCount[#, 3] == 0 && Total@ Rest@ Drop[DigitCount[#, 4], {3}] == 0 &] (* Michael De Vlieger, Oct 05 2015 *)

Join[{1, 5}, Flatten[Table[Select[FromDigits[#, 3]&/@Tuples[{1, 2}, n], Union[ IntegerDigits[ #, 4]] =={1, 3}&], {n, 20}]]] (* Harvey P. Dale, Jun 14 2016 *)

PROG

(PARI) is(n)=!setsearch(Set(digits(n, 3)), 0) && #setintersect(Set(digits(n, 4)), [0, 2])==0 \\ Charles R Greathouse IV, Oct 12 2015

(Python)

from gmpy2 import digits

def f1(n):

    s = digits(n, 3)

    m = len(s)

    for i in range(m):

        if s[i] == '0':

            return(int(s[:i]+'1'*(m-i), 3))

    return n

def f2(n):

    s = digits(n, 4)

    m = len(s)

    for i in range(m):

        if s[i] == '0':

            return(int(s[:i]+'1'*(m-i), 4))

        if s[i] == '2':

            return(int(s[:i]+'3'+'1'*(m-i-1), 4))

    return n

A262958_list = []

n = 1

for i in range(10**4):

    m = f2(f1(n))

    while m != n:

        n, m = m, f2(f1(m))

    A262958_list.append(m)

    n += 1 # Chai Wah Wu, Oct 30 2015

CROSSREFS

Cf. A207079, A258981, A261970.

Sequence in context: A201474 A078724 A191022 * A155757 A027674 A124307

Adjacent sequences:  A262955 A262956 A262957 * A262959 A262960 A262961

KEYWORD

nonn,base

AUTHOR

Robin Powell, Oct 05 2015

STATUS

approved

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Last modified September 18 18:20 EDT 2019. Contains 327178 sequences. (Running on oeis4.)