OFFSET
1,1
LINKS
T. D. Noe, Table of n, a(n) for n = 1..1000
EXAMPLE
k | divisors | concatenation
---+----------------+--------------
4 | (1) 2 (4) | 2
6 | (1) 2, 3 (6) | 23
9 | (1) 3 (9) | 3
21 | (1) 3, 7 (21) | 37
22 | (1) 2, 11 (22) | 211
25 | (1) 5 (25) | 5
33 | (1) 3, 11 (33) | 311
39 | (1) 3, 13 (39) | 313
MAPLE
with(numtheory):
for k from 2 to 1000 do:
v0:=divisors(k):
nn:=nops(v0):
if nn > 2 then
v1:=[seq(v0[j], j=2..nn-1)]:
v2:=cat(seq(convert(v1[n], string), n=1..nops(v1))):
v3:=parse(v2):
if isprime(v3) = true then lprint(k, v3) fi:
fi:
od: # Simon Plouffe
MATHEMATICA
fQ[n_] := PrimeQ@ FromDigits@ Most@ Rest@ Divisors@ n; Select[ Range[2, 320], fQ]
PROG
(Python)
from sympy import divisors, isprime
def ok(n):
s = "".join(str(d) for d in divisors(n)[1:-1])
return s != "" and isprime(int(s))
print([k for k in range(319) if ok(k)]) # Michael S. Branicky, Oct 01 2024
CROSSREFS
KEYWORD
nonn,base,changed
AUTHOR
Eric Angelini, Jul 19 2007
EXTENSIONS
Name edited by Michel Marcus, Mar 09 2023
STATUS
approved