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A066348 Numbers n such that phi(n+2) - 2*phi(n+1) + phi(n) = -n. 0
4, 6, 48, 33592, 44182, 1918396, 16975872, 129518496, 1098107800, 23181002496, 26187394752, 36959761320, 653669026776, 1857670810368 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The equation here is the difference equation (applied to phi) corresponding to the differential equation y" = -x (Hooke's law with constant = 1).

a(15) > 10^13. - Giovanni Resta, May 05 2017

LINKS

Table of n, a(n) for n=1..14.

EXAMPLE

Since phi(6) - 2*phi(5) + phi(4) = 2 - 2*4 + 2 = -4, 4 is a term of the sequence.

MATHEMATICA

Select[ Range[1, 10^7], EulerPhi[ # + 2] - 2*EulerPhi[ # + 1] + EulerPhi[ # ] == - # & ]

CROSSREFS

Cf. A000010 (phi).

Sequence in context: A134592 A306705 A165658 * A330978 A183369 A241159

Adjacent sequences:  A066345 A066346 A066347 * A066349 A066350 A066351

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Dec 19 2001

EXTENSIONS

More terms from Robert G. Wilson v, Dec 22 2001

a(7) and a(8) from Harry J. Smith, Feb 11 2010

a(9)-a(14) from Giovanni Resta, May 05 2017

STATUS

approved

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Last modified November 26 21:07 EST 2021. Contains 349344 sequences. (Running on oeis4.)