A081536 - OEIS

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A081536

Let f(n) be smallest number k which is a sum of n distinct numbers whose LCM is a multiple of k. Sequence gives triangle read by rows in which n-th row consists of those n numbers (row 2 is 0, 0 by convention).

1, 0, 0, 1, 2, 3, 1, 2, 4, 7, 1, 2, 3, 4, 5, 1, 2, 3, 4, 6, 8, 1, 2, 3, 4, 5, 6, 7, 1, 2, 3, 4, 5, 6, 8, 11, 1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 18, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13

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OFFSET

1,5

COMMENTS

Row 2k+1 consists of the first 2k+1 numbers, and row 2k consists of the first 2k numbers iff 2k+1 is not a power of a prime. - Charlie Neder, Feb 03 2019

LINKS

Table of n, a(n) for n=1..91.

FORMULA

The first n-2 members of row n > 2 are {1, 2, ..., n-2}. If the maximal prime powers dividing A081535(n) are all less than n, the ending terms are {n-1, A081535(n)-n*(n-1)/2}. Otherwise, they are {a, b} where either a or b is the largest prime power dividing A081535(n) and a + b = A081535(n) - (n-1)*(n-2)/2. - Charlie Neder, Feb 03 2019

EXAMPLE

Triangle begins:

0, 0;

1, 2, 3; (1+2+3 = 6 | 6 = lcm(1,2,3))

1, 2, 4, 7; (1+2+4+7 = 14 | 28 = lcm(1,2,4,7))

1, 2, 3, 4, 5;

...

CROSSREFS

Cf. A081535, A081537, A081538.

Sequence in context: A360476 A275728 A364057 * A297497 A152736 A139246

Adjacent sequences: A081533 A081534 A081535 * A081537 A081538 A081539

KEYWORD