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A137817 Cubeful "year numbers" (such that phi(n) = 2 phi(sigma(n)): A137815). 3
295569, 295947, 1586763, 1811079, 1964375, 2069469, 4473387, 5854375, 6820555, 7285923, 10936053, 12233457, 13260625, 18029709, 18052767, 21153663, 21576537, 21604131, 22182093, 22877451, 23744043, 25536875, 28340307, 34102775 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

See A137815 for general comments and references about "year numbers". This is the subsequence of cubeful elements of A137815, i.e. its intersection with A046099. As such, it is of course also a subsequence of A137816.

There are only 56 such numbers below 10^8.

LINKS

M. F. Hasler and Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 56 terms from M. F. Hasler)

PROG

(PARI) for( i=1, #A137816, vecmax( factor( A137816[i] )[, 2])>2 && print1(A137816[i]", "))

(PARI) for( i=1, #A046099, eulerphi(A046099[i])==2*eulerphi(sigma(A046099[i])) && print1( A046099[i] ", "))

(PARI) for( n=1, 10^9, issquarefree(n) && next; vecmax(factor(n)[, 2])>2 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))

CROSSREFS

Cf. A137815-A137819, A006872. A046099. A067704.

Sequence in context: A258527 A254919 A109031 * A137818 A303357 A251387

Adjacent sequences:  A137814 A137815 A137816 * A137818 A137819 A137820

KEYWORD

nonn

AUTHOR

R. K. Guy, R. J. Mathar and M. F. Hasler, Feb 11 2008

STATUS

approved

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Last modified June 21 19:12 EDT 2021. Contains 345365 sequences. (Running on oeis4.)