OFFSET
1,2
COMMENTS
Sophie-Germain-analog for numbers with odd digits.
Also numbers with the first digit an odd digit and the other digits in {5, 7, 9}. - David A. Corneth, May 15 2018
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
a(5(3^k-1)/2) = 10^k-1. - Giovanni Resta, Feb 22 2014
MATHEMATICA
Select[Range[1600], AllTrue[Join[IntegerDigits[#], IntegerDigits[ 2#+1]], OddQ]&] (* The program uses the AllTrue function from Mathematica version 10 *) (* Harvey P. Dale, May 15 2018 *)
PROG
(PARI) is(n)=#setminus(setunion(Set(digits(n)), Set(digits(2*n+1))), [1, 3, 5, 7, 9])==0 \\ Charles R Greathouse IV, May 15 2018
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Zak Seidov, Feb 21 2014
STATUS
approved