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 A317475 Numbers k such that k^2 | A038199(k). 1
 1, 16, 32, 64, 112, 128, 256, 395, 448, 512, 1024, 1093, 1168, 1368, 1472, 1792, 2013, 2048, 3279, 3344, 3511, 3968, 4096, 5472, 5696, 7168, 7651, 8192, 10533, 14209, 16384, 17488, 19674, 21672, 21888, 22953, 27552, 28672, 31599, 32768, 33883, 34905, 34976 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Serret proved in 1855 a generalization of Fermat's little theorem: for b >= 1, Sum_{d|k} mu(d)*b^(k/d) == 0 (mod k). This sequence includes numbers k such that k^2 divides the sum with base b=2. Includes all the powers of 2 above 8. An alternative generalization of Wieferich primes (A001220) which are the prime terms of this sequence. Also numbers k such that k | A059966(k). REFERENCES Wacław Sierpiński, Elementary Theory of Numbers, Elsevier, North Holland, 1988, page 217. LINKS Amiram Eldar, Table of n, a(n) for n = 1..250 Joseph-Alfred Serret, Théorème de Fermat généralisé, Nouvelles Annales de Mathématiques, Vol. 14 (1855), pp. 261-262. EXAMPLE 16 is in the sequence since Sum_{d|16} mu(d)*2^(16/d) = 65280 = 255 * 16^2. MATHEMATICA f[n_] := DivisorSum[n, MoebiusMu[#] * 2^(n/#) &]; Select[Range[1000], Divisible[f[#], #^2] &] PROG (PARI) isok(n) = frac(sumdiv(n, d, moebius(n/d)*(2^d-1))/n^2) == 0; \\ Michel Marcus, Jul 30 2018 CROSSREFS Cf. A000079, A001220, A038199, A059966, A077816, A182297. Sequence in context: A076468 A246550 A197917 * A335161 A239751 A261782 Adjacent sequences:  A317472 A317473 A317474 * A317476 A317477 A317478 KEYWORD nonn AUTHOR Amiram Eldar, Jul 29 2018 STATUS approved

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Last modified November 29 12:24 EST 2021. Contains 349416 sequences. (Running on oeis4.)