A116504 - OEIS

A116504

Number of distinct prime divisors of the concatenation of n,...,1.

0, 2, 2, 2, 3, 2, 2, 3, 3, 3, 2, 3, 3, 4, 5, 4, 6, 8, 4, 5, 4, 5, 4, 5, 6, 7, 5, 5, 7, 8, 3, 6, 5, 7, 8, 6, 4, 3, 6, 5, 8, 6, 3, 7, 6, 5, 7, 7, 3, 6, 3, 7, 9, 9, 3, 4, 4, 6, 3, 3, 5, 8, 5, 6, 7, 7, 4, 8, 8, 4, 8, 4, 7, 8, 10, 3, 7, 6, 4, 7, 7, 1, 3, 8, 3, 8, 5, 4, 5, 6, 11, 9, 6

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..93.

EXAMPLE

87654321 = 3*3*1997*4877, distinct prime divisors are 3, 1997 and 4877, hence a(8) = 3.

MATHEMATICA

b = {}; a = {}; Do[w = RealDigits[n]; w = First[w]; Do[PrependTo[a, w[[Length[w] - k + 1]]], {k, 1, Length[w]}]; p = FromDigits[a]; m = FactorInteger[p]; AppendTo[b, Length[m]], {n, 1, 30}]; b (* Artur Jasinski, Mar 30 2008 *)

Table[PrimeNu[FromDigits[Flatten[IntegerDigits/@Range[n, 1, -1]]]], {n, 95}] (* Harvey P. Dale, Oct 03 2015 *)

PROG

(PARI) {a=""; for(n=1, 58, a=concat(n, a); print1(omega(eval(a)), ", "))}

CROSSREFS

Cf. A116505.

Cf. A000422, A116504, A007908, A116505, A104759, A138789, A138790, A138793.

Sequence in context: A278597 A138789 A129654 * A186233 A226056 A104011

Adjacent sequences: A116501 A116502 A116503 * A116505 A116506 A116507

KEYWORD

nonn,base

AUTHOR

Parthasarathy Nambi, Mar 20 2006

EXTENSIONS

Edited and extended by Klaus Brockhaus, Mar 29 2006

Terms a(59)-a(93) from Sean A. Irvine, Nov 04 2009

STATUS

approved