A075348 - OEIS

A075348

Group the natural numbers such that the n-th group contains n terms and the group sum is the smallest possible prime.

2, 1, 4, 3, 5, 9, 6, 7, 8, 10, 11, 12, 13, 14, 17, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 32, 28, 29, 30, 31, 33, 34, 35, 37, 36, 38, 39, 40, 41, 42, 43, 44, 50, 45, 46, 47, 48, 49, 51, 52, 53, 54, 58, 55, 56, 57, 59, 60, 61, 62, 63, 64, 65, 71, 66, 67, 68, 69, 70, 72

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OFFSET

1,1

COMMENTS

Row sums (the primes) are in A075345. In case there is more than one way to write the given prime, e.g., A075345(3) = 3+5+9 = 3+6+8, the lexicographically smallest is to be chosen, here (3,5,9) rather than (3,6,8). - M. F. Hasler, Sep 26 2015

The flattened triangle is a permutation of the positive integers with inverse = A262663 and fixed points A262665.

LINKS

Reinhard Zumkeller, Rows n = 1..100 of triangle, flattened

Index entries for sequences that are permutations of the natural numbers

FORMULA

T(n,1)=A075346(n); T(n,n)=A075347(n); A075344(n) = Sum_{k=1..n} T(n,k). - Reinhard Zumkeller, Sep 26 2015

EXAMPLE

Triangle starts:

1, 4;

3, 5, 9;

6, 7, 8, 10;

11, 12, 13, 14, 17;