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A253137 a(n) = n*gcd(c(n), d(n)), where c(n) = composite numbers, d(n) = number of divisors of c(n). 0
1, 4, 12, 12, 10, 36, 14, 8, 9, 60, 22, 12, 26, 112, 15, 32, 17, 36, 38, 40, 21, 44, 23, 216, 50, 26, 216, 56, 58, 90, 62, 64, 33, 68, 35, 72, 74, 38, 312, 40, 82, 504, 86, 132, 45, 46, 94, 96, 49, 100, 612, 104, 159, 108, 55, 112, 570, 58, 118, 720, 61, 124, 63, 512, 390, 66, 134, 68, 138, 70, 852, 144, 219, 74, 150, 608, 77, 156, 948 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Occurrences of primes: 3 (17, 23, 61) in first 80 terms.

LINKS

Table of n, a(n) for n=1..79.

EXAMPLE

For n = 4: 4th composite number is 9. 9 has 3 divisors (1,3,9), thus gcd(9,3) * 4 = 12.

MATHEMATICA

Composites := Select[Range[2, 110], ! PrimeQ[#] &]; Composite[n_] := Last[Take[Composites, n]]; Table[GCD[Composite[n], DivisorSigma[0, Composite[n]]] n, {n, Length[Composites]}]

CROSSREFS

Cf. A002808, A000005.

Sequence in context: A238581 A063608 A074258 * A120213 A005886 A096442

Adjacent sequences:  A253134 A253135 A253136 * A253138 A253139 A253140

KEYWORD

nonn,easy

AUTHOR

Carlos Eduardo Olivieri, Dec 27 2014

STATUS

approved

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Last modified November 18 10:08 EST 2019. Contains 329261 sequences. (Running on oeis4.)