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A068401 Numbers n such that sigma(n)=phi(n+1)+phi(n-1). 0
2, 38, 62, 346, 1298, 7898, 22682, 24382, 93022, 108194, 143362, 171982, 192718, 264766, 587638, 986642, 1236898, 1441042, 1604422, 2228582, 4146434, 5070314, 5631718, 6687046, 10223918, 10695182, 12465158 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..27.

MATHEMATICA

Select[Range[2, 125*10^5], DivisorSigma[1, #]==Total[EulerPhi[#+{1, -1}]]&] (* Harvey P. Dale, Jan 22 2020 *)

PROG

(PARI) for(n=2, 12500000, if(sigma(n)==eulerphi(n+1)+eulerphi(n-1), print1(n, ", ")))

CROSSREFS

Sequence in context: A049487 A163792 A050899 * A173026 A294396 A075459

Adjacent sequences:  A068398 A068399 A068400 * A068402 A068403 A068404

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Mar 02 2002

EXTENSIONS

More terms from Rick L. Shepherd, Jul 04 2002

STATUS

approved

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Last modified September 19 03:31 EDT 2021. Contains 347550 sequences. (Running on oeis4.)