OFFSET
1,1
COMMENTS
a(14) > 10^10, if it exists. - Daniel Suteu, Apr 28 2024
EXAMPLE
26 is a term as 26 = 2 * 13 = "213" which is reverse is "312", and 312 is divisible by 26.
227501395 is a term as 227501395 = 5 * 11 * 17 * 23 * 71 * 149 = "511172371149" which in reverse is "941173271115", and 941173271115 is divisible by 227501395.
PROG
(Python)
from itertools import count, islice
from sympy import isprime, factorint
def ok(k): return not isprime(k) and int("".join(str(p)[::-1]*e for p, e in list(factorint(k).items())[::-1]))%k == 0
def agen(): yield from filter(ok, count(4))
print(list(islice(agen(), 7))) # Michael S. Branicky, Apr 13 2024
(Python)
from itertools import count, islice
from sympy import factorint
def A371696_gen(startvalue=4): # generator of terms >= startvalue
for n in count(max(startvalue, 4)):
f = factorint(n)
if sum(f.values()) > 1:
c = 0
for p in sorted(f, reverse=True):
a = pow(10, len(s:=str(p)), n)
q = int(s[::-1])
for _ in range(f[p]):
c = (c*a+q)%n
if not c:
yield n
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Scott R. Shannon, Apr 03 2024
EXTENSIONS
a(13) from Daniel Suteu, Apr 28 2024
STATUS
approved