login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A136975 Numbers k such that k and k^2 use only the digits 1, 2, 3, 5 and 7. 1
1, 5, 11, 15, 35, 111, 115, 235, 335, 715, 1235, 2715, 3335, 3511, 3515, 3711, 12335, 27115, 33335, 33515, 35711, 37115, 72335, 75711, 111235, 123335, 132335, 177515, 333335, 333515, 357115, 572115, 575515, 577515, 723335, 757115, 1233335, 1312335, 1323335, 3333335, 3333515, 3512511, 5227115, 5772115, 7233335, 11212115, 11277115, 11735515 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Generated with DrScheme.

Sequence is infinite; e.g., it contains 3...35 = (10^n-1)/3 + 2 for all n. - Robert Israel, Nov 24 2015

a(n) mod 100 can be only 11, 15 or 35 for n > 2. So if a(n) is a prime number, a(n) mod 100 = 11 for n > 2. Initial prime values of a(n) are 11, 3511 and 12375511 for n > 2. - Altug Alkan, Nov 25 2015

LINKS

Jonathan Wellons, Table of n, a(n) for n = 1..330

J. Wellons, Tables of Shared Digits

EXAMPLE

757313127132715^2 = 573523172527531752317223271225.

MAPLE

f2:= proc(n) local L; convert(convert(n^2, base, 10), set) intersect {4, 6, 8, 9, 0} = {} end proc:

S:= {0}: A:= {}:

for d from 1 to 8 do

  S:={seq(seq(10*s+j, j=[1, 2, 3, 5, 7]), s=S)};

  A:= select(f2, S) union A;

od:

sort(convert(A, list)); # Robert Israel, Nov 24 2015, corrected Sep 03 2020

MATHEMATICA

w = {1, 2, 3, 5, 7}; Select[Range[1, 10^7, 2], Union[IntegerDigits@ #, IntegerDigits[#^2], w] == w &] (* Michael De Vlieger, Nov 25 2015 *)

CROSSREFS

Cf. A001742, A034905.

Sequence in context: A034905 A031153 A136976 * A136973 A276037 A221743

Adjacent sequences:  A136972 A136973 A136974 * A136976 A136977 A136978

KEYWORD

base,nonn

AUTHOR

Jonathan Wellons (wellons(AT)gmail.com), Jan 22 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 19 06:18 EST 2022. Contains 350464 sequences. (Running on oeis4.)