A023693 Numbers with exactly 2 1's in ternary expansion.

4, 10, 12, 14, 16, 22, 28, 30, 32, 34, 36, 38, 42, 44, 46, 48, 50, 52, 58, 64, 66, 68, 70, 76, 82, 84, 86, 88, 90, 92, 96, 98, 100, 102, 104, 106, 108, 110, 114, 116, 126, 128, 132, 134, 136, 138, 140, 142, 144, 146, 150, 152, 154, 156, 158, 160, 166, 172, 174

Offset: 1

Author

Olivier Gérard

Keywords

• nonn
• base
• easy

Comments

From Bernard Schott, Jun 19 2023: (Start)

A003946 \ {1} is a subsequence since for m = 4*3^(k-1) with k >= 1, ternary expansion of m is 110...0 with (k-1) trailing 0's.

A034472 \ {2} is a subsequence since for m = 3^k + 1 with k >= 1, ternary expansion of m is 10...01 with (k-1) 0's between first and last 1's. (End)

Examples

			30 is a term since 30 = 1010_3 with exactly 2 1's.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A003946, A007089, A034472.

Programs

Mathematica

Select[ Range[ 162 ], (Count[ IntegerDigits[ #, 3 ], 1 ]==2)& ]

PARI

isok(k) = #select(x->(x==1), digits(k, 3)) == 2; \\ Michel Marcus, Jun 19 2023