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A137818
Non-biquadratefree "year numbers": phi(n) = 2 phi(sigma(n)) and p^4 | n for some p>1.
2
295569, 1811079, 1964375, 2069469, 4473387, 5854375, 10936053, 13260625, 18029709, 21576537, 22182093, 25536875, 35595625, 46404333, 49648383, 55094375, 57044817, 58650625, 67009923, 69166467, 72681875, 76106875
OFFSET
1,1
COMMENTS
See A137815 for general comments and references about "year numbers". This is the subsequence of elements of A137815 divisible by a biquadrateful number, i.e. its intersection with A046101 (numbers divisible by the 4th power of some prime). As such, it is of course also a subsequence of A137817 and a fortiori of A137816.
There are only 28 such numbers below 10^8.
LINKS
PROG
(PARI) for( i=1, #A137816, vecmax( factor( A137816[i])[, 2])>3 && 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])>3 || next; eulerphi(n)==2*eulerphi(sigma(n)) && print1(n", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved