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A066902 Integers k such that phi(prime(k)+1) = phi(prime(k)-1). 2
3, 5, 20, 156, 254, 377, 593, 1800, 5903, 5981, 7925, 18669, 19240, 41274, 48296, 135700, 146866, 228028, 234303, 251216, 407377, 654288, 802222, 886223, 938654, 1063412, 1072766, 1212140, 1238668, 1515063, 1609346, 2080991, 2097725, 2363130, 2408674, 2916514 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Integers k such that A008331(k) = A008330(k).

LINKS

Giovanni Resta, Table of n, a(n) for n = 1..675

FORMULA

a(n) = primepi(A067890(n)). - Giovanni Resta, Apr 06 2020

MATHEMATICA

Select[Range[1000000], EulerPhi[Prime[#]-1]==EulerPhi[Prime[#]+1]&] (* Harvey P. Dale, Feb 25 2012 *)

PROG

(PARI) isok(k) = my(p=prime(k)); eulerphi(p+1) == eulerphi(p-1); \\ Michel Marcus, Apr 06 2020

CROSSREFS

Cf. A000010, A008864, A006093, A008330, A008331, A067890.

Sequence in context: A197156 A171864 A256093 * A007363 A103991 A224994

Adjacent sequences:  A066899 A066900 A066901 * A066903 A066904 A066905

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jan 26 2002

EXTENSIONS

More terms from Harvey P. Dale, Feb 25 2012

More terms from Jinyuan Wang, Apr 05 2020

STATUS

approved

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Last modified September 29 17:04 EDT 2020. Contains 337432 sequences. (Running on oeis4.)