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 A349175 Odd numbers k for which gcd(k, A003961(k)) <> gcd(sigma(k), A003961(k)), where A003961(n) is fully multiplicative with a(prime(k)) = prime(k+1), and sigma is the sum of divisors function. 1
 15, 27, 35, 45, 57, 65, 75, 77, 87, 99, 105, 143, 165, 171, 175, 177, 189, 195, 205, 221, 225, 231, 237, 245, 255, 261, 267, 297, 301, 315, 323, 325, 327, 345, 351, 375, 385, 399, 405, 415, 417, 429, 437, 447, 459, 465, 485, 495, 513, 525, 531, 537, 539, 555, 567, 585, 595, 597, 605, 609, 615, 621, 627, 629, 645 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Odd numbers for which A348994(n) <> A349161(n). Equally, odd numbers such that A319626(n) <> A349164(n). LINKS Table of n, a(n) for n=1..65. Index entries for sequences computed from indices in prime factorization Index entries for sequences related to sigma(n) MATHEMATICA Select[Range[1, 645, 2], GCD[#1, #3] != GCD[#2, #3] & @@ {#, DivisorSigma[1, #], Times @@ Map[NextPrime[#1]^#2 & @@ # &, FactorInteger[#]]} &] (* Michael De Vlieger, Nov 11 2021 *) PROG (PARI) A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); }; isA349175(n) = if(!(n%2), 0, my(u=A003961(n)); gcd(u, sigma(n))!=gcd(u, n)); CROSSREFS Cf. A000203, A003961, A319626, A348994, A349161, A349164. Cf. A349169, A349174 (complement among the odd numbers). Sequence in context: A354714 A307854 A053177 * A145195 A096022 A097222 Adjacent sequences: A349172 A349173 A349174 * A349176 A349177 A349178 KEYWORD nonn AUTHOR Antti Karttunen, Nov 10 2021 STATUS approved

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Last modified August 4 07:02 EDT 2024. Contains 374905 sequences. (Running on oeis4.)