A238257 Numbers n such that n and 2n+1 use only odd decimal digits.

1, 3, 5, 7, 9, 15, 17, 19, 35, 37, 39, 55, 57, 59, 75, 77, 79, 95, 97, 99, 155, 157, 159, 175, 177, 179, 195, 197, 199, 355, 357, 359, 375, 377, 379, 395, 397, 399, 555, 557, 559, 575, 577, 579, 595, 597, 599, 755, 757, 759, 775, 777, 779, 795, 797, 799, 955, 957, 959, 975, 977, 979, 995, 997, 999, 1555, 1557, 1559, 1575, 1577, 1579

Offset: 1

Author

Zak Seidov, Feb 21 2014

Keywords

• nonn
• base
• easy

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

Crossrefs

Cf. A005384, A111153, A211162, A111173, A111176.

Programs

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 *)

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

Formula

a(5(3^k-1)/2) = 10^k-1. - Giovanni Resta, Feb 22 2014