A366958 - OEIS

A366958

Numbers whose difference between the largest and smallest digits is equal to 1.

10, 12, 21, 23, 32, 34, 43, 45, 54, 56, 65, 67, 76, 78, 87, 89, 98, 100, 101, 110, 112, 121, 122, 211, 212, 221, 223, 232, 233, 322, 323, 332, 334, 343, 344, 433, 434, 443, 445, 454, 455, 544, 545, 554, 556, 565, 566, 655, 656, 665, 667, 676, 677, 766, 767, 776, 778, 787, 788

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OFFSET

1,1

COMMENTS

The number of n-digit terms of this sequence is 17*A000225(n-1).

LINKS

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

MATHEMATICA

Select[Range[800], Max[d=IntegerDigits[#]]-Min[d]==1 &]

PROG

(PARI) isok(n) = my(d=digits(n)); vecmax(d) - vecmin(d) == 1; \\ Michel Marcus, Oct 30 2023

(Python)

def ok(n): return max(d:=list(map(int, str(n))))-min(d) == 1

print([k for k in range(800) if ok(k)]) # Michael S. Branicky, Oct 30 2023

(Python) # faster version for large terms

from itertools import count, islice, product

def agen(diff=1): # generator of terms; change diff for A366960-A366966

for digits in count(2):

s = set()

for lo in range(10-diff):

hi = lo + diff

allowed = list(range(lo, hi+1))

for p in product(allowed, repeat=digits):

if p[0]==0 or lo not in p or hi not in p: continue

s.add(int("".join(map(str, p))))

yield from sorted(s)

print(list(islice(agen(), 60))) # Michael S. Branicky, Oct 30 2023

CROSSREFS

Cf. A000225, A037904.

Cf. A010785 (difference = 0), A366959 (difference = 2), A366960 (difference = 3), A366961 (difference = 4), A366962 (difference = 5), A366963 (difference = 6), A366964 (difference = 7), A366965 (difference = 8), A366966 (difference = 9).

Sequence in context: A320170 A082927 A108965 * A341002 A175885 A061870

Adjacent sequences: A366955 A366956 A366957 * A366959 A366960 A366961

KEYWORD

nonn,base,easy

AUTHOR

Stefano Spezia, Oct 30 2023

STATUS

approved