A252481 Numbers whose set of digits is simply connected to 1.

1, 10, 11, 12, 21, 100, 101, 102, 110, 111, 112, 120, 121, 122, 123, 132, 201, 210, 211, 212, 213, 221, 231, 312, 321, 1000, 1001, 1002, 1010, 1011, 1012, 1020, 1021, 1022, 1023, 1032, 1100, 1101, 1102, 1110, 1111, 1112, 1120, 1121, 1122, 1123, 1132, 1200, 1201, 1202, 1203, 1210, 1211, 1212, 1213, 1220, 1221, 1222, 1223

Offset

1,2

Comments

"Simply connected" means that there must not be a "hole" in the set of digits. E.g., {1,2,4} would not be allowed since '3' is missing.

Links

Table of n, a(n) for n=1..59.

Prog

(PARI) is(n)={d=Set(digits(n)); d[1]==1 || (#d>1&&d[2]==1) || return; d[#d]==#d-!d[1]}
(Python)
def ok(n):
  s = set(str(n)); return '1' in s and len(s) == ord(max(s))-ord(min(s))+1
def aupto(nn): return [m for m in range(1, nn+1) if ok(m)]
print(aupto(1223)) # Michael S. Branicky, Jan 10 2021

Crossrefs

Cf. A032981, A050278, A033075, A010785, A108965, A134336, A252490.

Sequence in context: A235828 A102695 A376314 * A308854 A144582 A048024

Adjacent sequences: A252478 A252479 A252480 * A252482 A252483 A252484

Keyword

nonn,base

Author

M. F. Hasler, Dec 24 2014

Status

approved