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 A115374 Least prime p such that sigma(x)=sigma(p) has exactly n solutions. 2
 2, 11, 23, 179, 71, 167, 239, 431, 359, 503, 3167, 1511, 4679, 2687, 719, 9719, 4799, 16319, 5471, 10559, 1439, 26399, 24623, 3359, 15359, 3023, 7559, 6719, 2879, 26783, 10799, 13103, 5039, 6047, 45863, 29759, 61559, 18719, 27647, 99839, 22679, 68543 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For 11? It also appears that for each n there are an infinite number of primes p such that sigma(x)=sigma(p) has exactly n solutions. LINKS Donovan Johnson, Table of n, a(n) for n = 1..1199 MATHEMATICA s=DivisorSigma[1, Range]; t=Table[Length[Position[s, Prime[n]+1]], {n, PrimePi[Length[s]]}]; u=Union[t]; nLast=First[Complement[Range[u[[ -1]]], u]]-1; Flatten[Table[Prime[Position[t, n, 1, 1]], {n, nLast}]] PROG (PARI) sigv(n) =  select(i->sigma(i) == n, vector(n, i, i)); a(n) = {p = 2; while (#(sigv(p+1))! = n, p = nextprime(p+1)); p; } \\ Michel Marcus, May 01 2014 CROSSREFS Cf. A007368 (least k such that sigma(x)=k has n solutions), A066075 (number of solutions to sigma(x)=sigma(prime(n))). Sequence in context: A198277 A218046 A217309 * A078699 A291679 A239741 Adjacent sequences:  A115371 A115372 A115373 * A115375 A115376 A115377 KEYWORD nonn AUTHOR T. D. Noe, Jan 21 2006 STATUS approved

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Last modified April 3 23:48 EDT 2020. Contains 333207 sequences. (Running on oeis4.)