A050608 Numbers k such that base 7 expansion matches (0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*.

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 28, 29, 30, 31, 35, 36, 37, 38, 42, 43, 44, 45, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 77, 78, 79, 80, 84, 85, 86, 87, 91, 92, 93, 94, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113

Offset: 1

Author

Antti Karttunen, 1999

Keywords

• nonn
• easy
• base

Comments

49 does not divide C(2s-1,s) = A001700(s) (nor C(2s,s) = A000984(s), central column of Pascal's triangle) if and only if s is one of the terms in this sequence.

Links

• Index entries for 7-automatic sequences.

Crossrefs

Cf. A037461, A046097, A050607, A051382.

Programs

Perl

# For conv_x_base_n function, see A050607.
for($i=0; $i <= 1000; $i++) { if(("0" . conv_x_base_n($i,7)) =~ /^(0|1|2|3)*((0|1|2)(4|5|6))?(0|1|2|3)*$/) { print $i, ","; } }

Extensions

a(1)=0 inserted by Georg Fischer, Jun 26 2021