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A269525 a(1) = 1, a(n) is the sum of m < n for which a(m) has at most as many divisors as n. 1
1, 1, 3, 6, 6, 15, 6, 28, 6, 37, 16, 66, 16, 47, 61, 100, 45, 125, 45, 162, 94, 115, 45, 240, 45, 137, 163, 306, 98, 347, 128, 365, 252, 252, 252, 456, 128, 252, 252, 477, 128, 558, 128, 437, 481, 341, 128, 819, 128, 572, 387, 623, 128, 988 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

LINKS

Peter Kagey, Table of n, a(n) for n = 1..1000

EXAMPLE

a(1) = 1;

a(2) = 1 because a(1) has at most as many divisors as 2;

a(3) = 3 because a(1) and a(2) have at most as many divisors as 3;

a(4) = 6 because a(1), a(2), and a(3) have at most as many divisors as 4;

a(5) = 6 because a(1), a(2), and a(3) have at most as many divisors as 5.

MATHEMATICA

a = {1}; Do[d = DivisorSigma[0, n]; AppendTo[a, Total@ Select[Range[n - 1], DivisorSigma[0, a[[#]]] <= d &]], {n, 2, 54}]; a (* Michael De Vlieger, Mar 24 2016 *)

PROG

(Java)

int[] terms = new int[100];

terms[0] = 1;

for (int i = 1; i < 100; i++) {

    int count = 0;

    for (int j = 0; j < i; j++) {

        if (divisors(terms[j]) <= divisors(i+1)) {

            count = count + j + 1;

        }

    }

    terms[i] = count;

}

(PARI) lista(nn) = {va = vector(nn); print1(va[1] = 1, ", "); for (n=2, nn, va[n] = sum(k=1, n-1, k*(numdiv(va[k]) <= numdiv(n))); print1(va[n], ", "); ); } \\ Michel Marcus, Feb 29 2016

CROSSREFS

Sequence in context: A119306 A107972 A238775 * A036252 A103463 A265026

Adjacent sequences:  A269522 A269523 A269524 * A269526 A269527 A269528

KEYWORD

easy,nonn

AUTHOR

Alec Jones, Feb 29 2016

STATUS

approved

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Last modified November 17 16:03 EST 2019. Contains 329238 sequences. (Running on oeis4.)