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 A067519 Numbers k such that k^2 + 1 is composite and phi(k^2 + 1) == 0 (mod k). 1
 8, 32, 50, 64, 128, 192, 216, 336, 360, 900, 1000, 1152, 1250, 1280, 1344, 1408, 1800, 2450, 2880, 4096, 5440, 6528, 7564, 9216, 9800, 11008, 12544, 13824, 14450, 14976, 16576, 18432, 20000, 21420, 21440, 24200, 25675, 36000, 36288, 43778, 46656 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If k^2 + 1 is prime, trivially phi(k^2 + 1) == 0 (mod k). LINKS Amiram Eldar, Table of n, a(n) for n = 1..500 (terms 1..300 from Donovan Johnson) MATHEMATICA n2Q[n_]:=Module[{c=n^2+1}, CompositeQ[c]&&Divisible[EulerPhi[c], n]]; Select[Range[50000], n2Q] (* Harvey P. Dale, Apr 16 2015 *) PROG (PARI) for(n=1, 46656, m=n^2+1; if(isprime(m)==0, if(eulerphi(m)%n==0, print1(n ", ")))) \\ Donovan Johnson, Nov 14 2013 CROSSREFS Cf. A000010, A066820. Sequence in context: A127988 A129749 A005879 * A253295 A290960 A009245 Adjacent sequences: A067516 A067517 A067518 * A067520 A067521 A067522 KEYWORD nonn AUTHOR Benoit Cloitre, Feb 22 2002 STATUS approved

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Last modified June 6 03:09 EDT 2023. Contains 363138 sequences. (Running on oeis4.)