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A129292 Number of divisors of n^4 - 1 that are not greater than n. 5
1, 1, 2, 2, 4, 2, 6, 4, 5, 3, 8, 3, 10, 4, 6, 4, 12, 4, 13, 4, 11, 6, 14, 3, 10, 6, 12, 6, 17, 3, 16, 7, 10, 9, 13, 4, 18, 7, 11, 4, 22, 3, 26, 8, 9, 7, 23, 5, 18, 7, 13, 6, 25, 4, 24, 8, 21, 6, 18, 3, 18, 10, 12, 14, 16, 4, 26, 8, 17, 7, 31, 5, 30, 6, 11, 13, 26, 7, 25, 6, 16, 10, 35, 4, 18, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) = #{d: d<=n and A123865(n) mod d = 0};

a(n)>1 for n>2, see A129293 for m such that a(m)=2: a(A129293(n))=2.

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..1000

EXAMPLE

a(100) = #{1,3,9,11,33,73,99} = 7.

MAPLE

f:= n -> nops(select(`<=`, numtheory:-divisors(n^4-1), n)):

1, seq(f(n), n=2..100); # Robert Israel, Sep 21 2014

MATHEMATICA

Table[Count[Divisors[n^4-1], _?(#<=n&)], {n, 90}] (* Harvey P. Dale, Aug 13 2014 *)

PROG

(PARI) a(n) = if (n==1, 1, sumdiv(n^4-1, d, d <= n); \\ Michel Marcus, Sep 21 2014

CROSSREFS

Cf. A129294, A129296.

Sequence in context: A091279 A096002 A082175 * A126606 A285699 A278229

Adjacent sequences:  A129289 A129290 A129291 * A129293 A129294 A129295

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Apr 09 2007

STATUS

approved

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Last modified March 8 19:52 EST 2021. Contains 341953 sequences. (Running on oeis4.)