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A080767 A unitary phi reciprocal amicable number: consider two different numbers a, b which satisfy the following equation for some integer k: uphi(a)=uphi(b)=1/k*a*b/(a-b); or equivalently, 1/uphi(a)=1/uphi(b)=k*(-1/a+1/b); sequence gives b numbers. 2
1, 3, 12, 20, 220, 144, 240, 5060, 5520, 5520, 10800, 11520, 8928, 15120, 31680, 33984, 56576, 60372, 39168, 65280, 80640, 149760, 149760, 169920, 281600, 398200, 664092, 669600, 940896, 1235520 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Here uphi(n)=A047994(n) is the unitary totient function: if n = Product p_i^e_i, uphi(n) = Product (p_i^e_i - 1).

LINKS

Table of n, a(n) for n=0..29.

CROSSREFS

Cf. A047994, A080766, A080768, A067739, A067741.

Sequence in context: A143268 A193558 A256131 * A043465 A074276 A055041

Adjacent sequences: A080764 A080765 A080766 * A080768 A080769 A080770

KEYWORD

nonn

AUTHOR

Yasutoshi Kohmoto

EXTENSIONS

Kohmoto found 2nd, 6th, 13th, 25th terms. Dean Hickerson calculated the other terms.

STATUS

approved

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Last modified January 27 20:21 EST 2023. Contains 359849 sequences. (Running on oeis4.)