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A071806 Number of pairs (x,y) such that prime(x) + prime(y) = y*tau(x) + x*tau(y), 1<=x<=y<=n. 0
0, 0, 0, 0, 2, 2, 2, 2, 2, 3, 3, 4, 4, 4, 4, 4, 5, 6, 7, 7, 7, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 10, 11, 12, 12, 12, 15, 18, 18, 19, 19, 20, 20, 20, 20, 20, 20, 20, 21, 21, 22, 22, 23, 23, 23, 23, 23, 23, 24, 24, 24, 25, 26, 26, 26, 26, 28, 28, 29, 29, 29, 29, 29, 30, 31, 31, 31, 31, 31 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..80.

PROG

(PARI) for(n=1, 130, print1(sum(i=1, n, sum(j=1, i, if(prime(i)+prime(j)-j*numdiv(i)-i*numdiv(j), 0, 1))), ", "))

CROSSREFS

Cf. A000005.

Sequence in context: A304884 A286707 A025788 * A025781 A218379 A242763

Adjacent sequences:  A071803 A071804 A071805 * A071807 A071808 A071809

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Jun 06 2002

STATUS

approved

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Last modified April 14 22:47 EDT 2021. Contains 342971 sequences. (Running on oeis4.)