OFFSET
1,1
COMMENTS
00 -> 0 is not allowed, else all digits will not appear in the concatenation of terms. For example, a(198)..a(201) = 198, 19920, 0, 2 and not 198, 192, 0, 2. - Michael S. Branicky, Dec 03 2021
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..10000 (24 terms corrected in terms 1..10000 from Reinhard Zumkeller)
FORMULA
GCD(a(n), a(n+1)) > 1.
EXAMPLE
. a(n) | 12,3,45,6,78,9,1011,12,1314,15,1617,18,192,0,2,12,2,2,32,4,2,52
--------+----------------------------------------------------------------
. gcd | 3 3 3 6 3 3 3 6 3 3 3 6 192 2 2 2 2 2 4 2 2 .
PROG
(Haskell)
a258227 n = a258227_list !! (n-1)
a258227_list = f 12 1 (map toInteger $ tail a007376_list) where
f x y (d:ds) | gcd x y > 1 = y : f y d ds
| otherwise = f x (10 * y + d) ds
(Python)
from math import gcd
from itertools import count
def diggen():
for k in count(1): yield from list(map(int, str(k)))
def aupton(terms):
g = diggen()
alst, aset = [12], {12}
_, _, nxtd, nxtnxtd = next(g), next(g), next(g), next(g)
for n in range(2, terms+1):
an, nxtd, nxtnxtd = nxtd, nxtnxtd, next(g)
while gcd(an, alst[-1]) == 1 or nxtd == nxtnxtd == 0:
an, nxtd, nxtnxtd = int(str(an) + str(nxtd)), nxtnxtd, next(g)
alst.append(an); aset.add(an)
return alst
print(aupton(70)) # Michael S. Branicky, Dec 03 2021
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, May 23 2015
STATUS
approved