A163838 - OEIS

A163838

a(n) = (n-th composite) * (number of nontrivial divisors of n-th composite).

4, 12, 16, 9, 20, 48, 28, 30, 48, 72, 80, 42, 44, 144, 25, 52, 54, 112, 180, 128, 66, 68, 70, 252, 76, 78, 240, 252, 176, 180, 92, 384, 49, 200, 102, 208, 324, 110, 336, 114, 116, 600, 124, 252, 320, 130, 396, 272, 138, 420, 720, 148, 300, 304, 154, 468, 640, 243

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OFFSET

1,1

COMMENTS

The trivial divisors of the n-th composite are 1 and the n-th composite.

LINKS

Table of n, a(n) for n=1..58.

FORMULA

a(n) = A002808(n)*A144925(n).

EXAMPLE

a(1) = 4 (= 4*1);

a(2) = 12 (= 6*2);

a(3) = 16 (= 8*2);

a(4) = 9 (= 9*1);

a(5) = 20 (= 10*2);

a(6) = 48 (= 12*4).

MAPLE

A002808 := proc(n) option remember; local a; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do: end if; end proc: A070824 := proc(n) numtheory[tau](n)-2 ; end: A144925 := proc(n) A070824(A002808(n)) ; end: A163838 := proc(n) A144925(n)*A002808(n) ; end: seq(A163838(n), n=1..80) ; # R. J. Mathar, Oct 10 2009

MATHEMATICA

# (DivisorSigma[0, #]-2)&/@Select[Range[100], CompositeQ] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jan 23 2021 *)

CROSSREFS

Cf. A002808, A070824, A144925.

Sequence in context: A224785 A195547 A335528 * A228091 A157849 A137257

Adjacent sequences: A163835 A163836 A163837 * A163839 A163840 A163841

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Aug 05 2009, Aug 06 2009

EXTENSIONS

56 replaced with 112, 310 replaced with 320, and 468 inserted by R. J. Mathar, Oct 10 2009

STATUS

approved