A106708 a(n) is the concatenation of its nontrivial divisors.

0, 0, 0, 2, 0, 23, 0, 24, 3, 25, 0, 2346, 0, 27, 35, 248, 0, 2369, 0, 24510, 37, 211, 0, 2346812, 5, 213, 39, 24714, 0, 23561015, 0, 24816, 311, 217, 57, 234691218, 0, 219, 313, 24581020, 0, 23671421, 0, 241122, 35915, 223, 0, 23468121624, 7, 251025, 317

Offset

1,4

Links

Klaus Brockhaus, Table of n, a(n) for n=1..5000

Formula

a(n) = A037279(n) * A010051(n). - R. J. Mathar, Aug 01 2007

Maple

A106708 := proc(n) local dvs ; if isprime(n) or n = 1 then 0; else dvs := [op(numtheory[divisors](n) minus {1, n} )] ; dvs := sort(dvs) ; cat(op(dvs)) ; fi ; end: seq(A106708(n), n=1..80) ; # R. J. Mathar, Aug 01 2007

Mathematica

Table[If[CompositeQ[n], FromDigits[Flatten[IntegerDigits/@Rest[ Most[ Divisors[ n]]]]], 0], {n, 60}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jun 22 2020 *)

Prog

(PARI)
{map(n) = local(d); d=divisors(n); if(#d<3, 0, d[1]=""; eval(concat(vecextract(d, concat("..", #d-1)))))}
for(n=1, 51, print1(map(n), ", ")) /* Klaus Brockhaus, Aug 05 2007 */
(Haskell)
a106708 1           = 0
a106708 n
   | a010051 n == 1 = 0
   | otherwise = read $ concat $ (map show) $ init $ tail $ a027750_row n
-- Reinhard Zumkeller, May 01 2012
(Python)
from sympy import divisors
def a(n):
  nontrivial_divisors = [d for d in divisors(n)[1:-1]]
  if len(nontrivial_divisors) == 0: return 0
  else: return int("".join(str(d) for d in nontrivial_divisors))
print([a(n) for n in range(1, 52)]) # Michael S. Branicky, Dec 31 2020

Crossrefs

Cf. A037278, A120712, A037279, A131983 (records), A131984 (where records occur).

Cf. A027750, A010051, A037285, A037277, A163870.

Sequence in context: A254042 A368014 A009378 * A138551 A133490 A051728

Adjacent sequences: A106705 A106706 A106707 * A106709 A106710 A106711

Keyword

nonn,base

Author

N. J. A. Sloane, Jul 20 2007

Extensions

More terms from R. J. Mathar and Klaus Brockhaus, Aug 01 2007

Name edited by Michael S. Branicky, Dec 31 2020

Status

approved