A263118 -id:A263118 - cp's OEIS frontend

A263152 a(n) is the greatest common unitary divisor of the friendly pairs, A050972(n) and A050973(n).

1, 5, 1, 1, 1, 1, 11, 13, 17, 1, 1, 19, 3, 23, 3, 25, 29, 1, 31, 1, 37, 41, 5, 43, 47, 7, 53, 3, 1, 55, 7, 2, 1, 59, 61, 9, 65, 67, 71, 9, 73, 11, 79, 83, 85, 11, 5, 5, 89, 11, 13, 95, 97, 101, 103, 13, 11, 107, 109, 113, 115, 4, 121, 17, 7, 125, 13, 127, 131

Offset: 1

Michel Marcus, Oct 11 2015

nonn

Dividing both A050972(n) and A050973(n) by a "greater than 1" divisor of a(n), if any, will give a smaller friendly pair.

If a(n) is greater than 1, dividing both A050972(n) and A050973(n) will give a primitive friendly pair.

			The greatest common unitary divisor of the first friendly pair (6, 28) is 1, hence a(1) = 1.

Michel Marcus, Table of n, a(n) for n = 1..10000

Cf. A050972, A050973, A263118.

Cf. A165430 (greatest common unitary divisor).

udivs(n) = {my(d = divisors(n)); select(x->(gcd(x, n/x)==1), d);}
ugcd(x,y) = vecmax(setintersect(udivs(x), udivs(y)));
lista(vp, vg) = {for (n=1, #vp, print1(ugcd(vp[n], vg[n])", ")); } \\ where vp and vg are A050972 and A050973

a(n) = A165430(A050972(n), A050973(n)).

a(A263118(n)) = 1, the primitive friendly pairs.

cp's OEIS Frontend

A263152 a(n) is the greatest common unitary divisor of the friendly pairs, A050972(n) and A050973(n).

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