A328637 -id:A328637 - cp's OEIS frontend

A328638 a(n) is the sum of m such that 2 <= m <= n and gpf(m) = gpf(n), where gpf(i) is the greatest prime factor of i (A006530), with a(1) = 1.

1, 2, 3, 6, 5, 9, 7, 14, 18, 15, 11, 30, 13, 21, 30, 30, 17, 48, 19, 50, 42, 33, 23, 72, 75, 39, 99, 70, 29, 105, 31, 62, 66, 51, 105, 135, 37, 57, 78, 145, 41, 147, 43, 110, 190, 69, 47, 183, 196, 240, 102, 130, 53, 237, 165, 252, 114, 87, 59, 300

Offset: 1

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J. Stauduhar, Oct 22 2019

nonn
easy

For n >= 2, a(n) is the sum of the terms that precede n on the row, of the A125624 array, that contains n.

			5, 10, 15 and 20 have same gpf as 20, so a(20) = 5 + 10 + 15 + 20 = 50.

Cf. A006530 (gpf), A125624, A078899, A328637.

gpf(n)={my(f=factor(n)[,1]); f[#f]}
a(n)={if(n<=1, n==1, my(t=gpf(n)); sum(i=2, n, if(gpf(i)==t, i, 0)))} \\ Andrew Howroyd, Oct 28 2019

cp's OEIS Frontend

A328638 a(n) is the sum of m such that 2 <= m <= n and gpf(m) = gpf(n), where gpf(i) is the greatest prime factor of i (A006530), with a(1) = 1.

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