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A068473 Numbers n such that phi((prime(n)+1)/2)=sigma(n). 1
31, 51, 77, 87, 158, 184, 297, 308, 573, 621, 766, 786, 799, 826, 1167, 1330, 1946, 2030, 2280, 3058, 3213, 5015, 5093, 5271, 5374, 8307, 8813, 9730, 10364, 10557, 11229, 12750, 13462, 14145, 15807, 20606, 23115, 24633, 24795, 26400, 28015 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..100

MATHEMATICA

Select[Range[2, 30000], EulerPhi[(Prime[#]+1)/2]==DivisorSigma[1, #]&] (* Harvey P. Dale, May 01 2015 *)

PROG

(PARI) for(n=2, 45000, if(eulerphi((prime(n)+1)/2)==sigma(n), print1(n, ", ")))

CROSSREFS

Sequence in context: A288291 A248904 A068779 * A275628 A176507 A163321

Adjacent sequences:  A068470 A068471 A068472 * A068474 A068475 A068476

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Mar 10 2002

STATUS

approved

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Last modified August 10 04:38 EDT 2020. Contains 336368 sequences. (Running on oeis4.)