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A160691 a(n) = the number of divisors of A160689(n) = the number of divisors of A160690(n). 5
1, 2, 2, 2, 4, 2, 2, 4, 2, 2, 4, 2, 2, 4, 2, 4, 2, 4, 4, 4, 2, 4, 4, 4, 2, 4, 6, 4, 6, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 4, 4, 2, 4, 4, 2, 4, 2, 4, 4, 4, 2, 2, 4, 4, 2, 4, 4, 4, 2, 4, 2, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 2, 4, 2, 4, 4, 2, 4, 4, 4, 4, 4, 4, 4, 4, 2, 4, 2, 4, 4, 2, 4, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Contribution from Farideh Firoozbakht, May 28 2009: (Start)

For the first 200000 natural numbers n, a(n) is in the set {1,2,4,6,8,12}

and in fact we have:

For one number n, A160691(n)=1.

For 13 numbers n, A160691(n)=12 (see the sequence A158963).

For 4785 numbers n, A160691(n)=6.

For 6706 numbers n, A160691(n)=8.

For 26790 numbers n, A160691(n)=2.

For 161705 numbers n, A160691(n)=4.

Also n=2 is the only number n (less than 200000) that a(n)=a(n+1)=a(n+2)=2.

and for the 53 consecutive numbers 64833, 64834, ..., 64885 we have a(n)=4. (End)

LINKS

Table of n, a(n) for n=1..105.

MATHEMATICA

Contribution from Farideh Firoozbakht, May 28 2009: (Start)

c[1]=1; c[n_]:=c[n]=(s=Sum[c[k], {k, n-1}]; For[m=1, DivisorSigma[0, m]!=

DivisorSigma[0, s+m], m++ ]; m); a[n_]:=a[n]=DivisorSigma[0, c[n]];

Table[a[n], {n, 105}] (End)

CROSSREFS

A160689, A160690

Cf. A158963, A158964. [From Farideh Firoozbakht, May 28 2009]

Sequence in context: A279409 A102445 A027389 * A049716 A188903 A066671

Adjacent sequences:  A160688 A160689 A160690 * A160692 A160693 A160694

KEYWORD

nonn

AUTHOR

Leroy Quet, May 24 2009

EXTENSIONS

More terms from Farideh Firoozbakht, May 28 2009

STATUS

approved

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Last modified May 25 01:01 EDT 2017. Contains 287008 sequences.