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 A069953 Composite n such that (n-1)*phi(n) is a perfect square. 2
 10, 28, 51, 170, 243, 246, 946, 1128, 1281, 1353, 1695, 2431, 4336, 4411, 4625, 4803, 7501, 7936, 8625, 11914, 12545, 13255, 15051, 16385, 24643, 27870, 29404, 31828, 33490, 36751, 39676, 47046, 52801, 53291, 55471, 58807, 66249, 72076, 74061, 81676, 90775 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If k>1 k*phi(k) is not a perfect square. Trivially, if p is prime (p-1)*phi(p) is a perfect square. LINKS Donovan Johnson, Table of n, a(n) for n = 1..1000 MATHEMATICA psQ[n_]:=CompositeQ[n]&&IntegerQ[Sqrt[(n-1)EulerPhi[n]]]; Select[ Range[ 100000], psQ] (* Harvey P. Dale, Nov 08 2017 *) PROG (PARI) for(n=2, 120000, if(frac(sqrt((n-1+isprime(n))*eulerphi(n)))==0, print1(n, ", "))) CROSSREFS Sequence in context: A088407 A267012 A273195 * A113746 A177720 A117464 Adjacent sequences: A069950 A069951 A069952 * A069954 A069955 A069956 KEYWORD easy,nonn AUTHOR Benoit Cloitre, Apr 27 2002 STATUS approved

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Last modified April 12 22:48 EDT 2024. Contains 371639 sequences. (Running on oeis4.)