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A001494
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Numbers n such that phi(n) = phi(n+2).
(Formerly M3293 N1328)
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8
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4, 7, 8, 10, 26, 32, 70, 74, 122, 146, 308, 314, 386, 512, 554, 572, 626, 635, 728, 794, 842, 910, 914, 1015, 1082, 1226, 1322, 1330, 1346, 1466, 1514, 1608, 1754, 1994, 2132, 2170, 2186, 2306, 2402, 2426, 2474, 2590, 2642, 2695, 2762, 2906, 3242, 3314
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| If p and 2p-1 are odd primes then 2(2p-1) is a solution of the equation. Other terms (7,8,32,70,...) are not of this form.
There are approximately 506764125 terms under 10^12. - Jud McCranie. Feb 13 2012
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REFERENCES
| D. M. Burton, Elementry Number Theory, section 7-2.
R. K. Guy, Unsolved Problems Number Theory, Sect. B36.
V. L. Klee, Jr., Some remarks on Euler's totient function, Amer. Math. Monthly, 54 (1947), 332.
L. Moser, Some equations involving Euler's totient function, Amer. Math. Monthly, 56 (1949), 22-23.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| T. D. Noe and Jud McCranie, Table of n, a(n) for n = 1..10000 (T. D. Noe supplied 1000 terms)
M. F. Hasler, Table of n, a(n) for n = 1..17286. (Terms up to 10^7.)
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MATHEMATICA
| Select[Range[3500], EulerPhi[#]==EulerPhi[#+2]&] (* From Harvey P. Dale, Apr 24 2011 *)
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PROG
| (PARI) op=[0, c=0]; for( n=1, 1e7, if( op[bittest(n, 0)+1]+0==op[bittest(n, 0)+1]=eulerphi(n), write("../OEIS/b001494.txt", c++, " "n-2))) \\ - M. F. Hasler, Jan 05 2011
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CROSSREFS
| Cf. A000010, A001274.
Sequence in context: A175008 A084791 A186712 * A092214 A128373 A080578
Adjacent sequences: A001491 A001492 A001493 * A001495 A001496 A001497
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KEYWORD
| nonn,nice,changed
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu), Dec 24 1999
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