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 A240667 a(n) is the GCD of the solutions x of sigma(x) = n; sigma(n) = A000203(n) = sum of divisors of n. 8
 1, 0, 2, 3, 0, 5, 4, 7, 0, 0, 0, 1, 9, 13, 8, 0, 0, 1, 0, 19, 0, 0, 0, 1, 0, 0, 0, 12, 0, 29, 1, 1, 0, 0, 0, 22, 0, 37, 18, 27, 0, 1, 0, 43, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 49, 0, 0, 1, 0, 61, 32, 0, 0, 0, 0, 67, 0, 0, 0, 1, 0, 73, 0, 0, 0, 45, 0, 1, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS From n=1 to 5, the least integers such that a(x)=n, depending on if singletons (see A007370 and A211656) are accepted or not, are 1, 3, 4, 7, 6 or 12, 126, 124, 210, 22152. Is it possible to find an integer n such that a(n) = 6? LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 FORMULA a(A007369(n)) = 0. EXAMPLE There are no integers such that sigma(x)=2, so a(2)=0. There is a single integer, x=2, such that sigma(x)=3, so a(3)=2. There are 2 integers, x=6 and 11, such that sigma(x)=12, their gcd is 1, so a(12)=1. MAPLE A240667 := n -> igcd(op(select(k->sigma(k)=n, [\$1..n]))): seq(A240667(n), n=1..82); # Peter Luschny, Apr 13 2014 MATHEMATICA a[n_] := GCD @@ Select[Range[n], DivisorSigma[1, #] == n&]; Array[a, 100] (* Jean-François Alcover, Jul 30 2018 *) PROG (PARI) sigv(n) =  select(i->sigma(i) == n, vector(n, i, i)); a(n) = {v = sigv(n); if (#v == 0, 0, gcd(v)); } CROSSREFS Cf. A000203, A007369, A007370, A211656, A241479 (a variant). Sequence in context: A277516 A322333 A346615 * A051444 A299762 A057637 Adjacent sequences:  A240664 A240665 A240666 * A240668 A240669 A240670 KEYWORD nonn AUTHOR Michel Marcus, Apr 10 2014 STATUS approved

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Last modified December 2 08:31 EST 2021. Contains 349437 sequences. (Running on oeis4.)