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A131904 Smallest positive integer k with the same number of divisors as the n-th integer for which such a k exists. 0
2, 2, 2, 6, 4, 6, 2, 2, 6, 6, 2, 12, 2, 12, 6, 6, 2, 4, 6, 6, 12, 2, 24, 2, 12, 6, 6, 6, 2, 6, 6, 24, 2, 24, 2, 12, 12, 6, 2, 4, 12, 6, 12, 2, 24, 6, 24, 6, 6, 2, 2, 6, 12, 6, 24, 2, 12, 6, 24, 2, 60, 2, 6, 12, 12, 6, 24, 2, 48, 16, 6, 2, 60, 6, 6, 6, 24, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..78.

FORMULA

a(n)=min(k>0, k has the same number of divisors as A131903(n))

EXAMPLE

a(4)=6 because A131903(4)=8, which has four divisors, and 6 is the least positive integer with four divisors

MATHEMATICA

Clear[tmp]; Function[n, If[Head[ #1] === tmp, #1 = n; Unevaluated[Sequence[]], # ] & [tmp[DivisorSigma[0, n]]]] /@ Range[64]

PROG

(PARI) lista(nn) = {for (n=1, nn, my(nd = numdiv(n)); for (k=1, n-1, if (numdiv(k) == nd, print1(k, ", "); break); ); ); } \\ Michel Marcus, Apr 03 2015

CROSSREFS

Cf. A069822, A131902-A131908.

Sequence in context: A227550 A286384 A099259 * A278264 A232114 A038074

Adjacent sequences:  A131901 A131902 A131903 * A131905 A131906 A131907

KEYWORD

easy,nonn

AUTHOR

Peter Pein (petsie(AT)dordos.net), Jul 26 2007

EXTENSIONS

More terms from Michel Marcus, Apr 03 2015

STATUS

approved

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Last modified August 18 13:25 EDT 2019. Contains 326100 sequences. (Running on oeis4.)