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 A134605 Composite numbers such that the square root of the sum of squares of their prime factors (with multiplicity) is an integer. 20
 16, 48, 81, 320, 351, 486, 512, 625, 1080, 1260, 1350, 1375, 1792, 1836, 2070, 2145, 2175, 2401, 2730, 2772, 3072, 3150, 3510, 4104, 4305, 4625, 4650, 4655, 4998, 5880, 6000, 6174, 6545, 7098, 7128, 7182, 7650, 7791, 7889, 7956, 9030, 9108, 9295, 9324 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Hieronymus Fischer, Table of n, a(n) for n = 1..10000 EXAMPLE a(2)=48 since 48=2*2*2*2*3 and sqrt(4*2^2+3^2)=sqrt(25)=5. MATHEMATICA srssQ[n_]:=IntegerQ[Sqrt[Total[Flatten[Table[#[[1]], #[[2]]]&/@ FactorInteger[ n]]^2]]]; Select[Range[10000], CompositeQ[#]&&srssQ[#]&] (* Harvey P. Dale, Jan 22 2019 *) PROG (PARI) is(n)=my(f=factor(n)); issquare(sum(i=1, #f~, f[i, 1]^2*f[i, 2])) && !isprime(n) && n>1 \\ Charles R Greathouse IV, Apr 29 2015 CROSSREFS Cf. A001597, A025475, A134333, A134344, A134376, A134600, A134602, A134608, A134611, A134616, A134618, A134620. Sequence in context: A069084 A084112 A050428 * A035008 A189972 A023648 Adjacent sequences:  A134602 A134603 A134604 * A134606 A134607 A134608 KEYWORD nonn AUTHOR Hieronymus Fischer, Nov 11 2007 STATUS approved

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Last modified October 15 17:24 EDT 2019. Contains 328037 sequences. (Running on oeis4.)