cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A377992 Irregular triangle giving on row n all antiderivatives of A024451(n), for n >= 2.

Original entry on oeis.org

6, 30, 58, 210, 435, 507, 2310, 8435, 21827, 29233, 30030, 39030, 62762, 69914, 76442, 78874, 510510, 1342785, 1958673, 9699690, 28235362, 223092870, 975351895, 1527890095, 1885679383, 2189118743, 2329696457, 2338611863, 3485765789, 4586671213, 5453593183, 5472849253, 5674340053, 8071055747, 8931775397, 9332889127
Offset: 2

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Author

Antti Karttunen, Nov 19 2024

Keywords

Comments

Row n lists in ascending order all numbers k whose arithmetic derivative k' [A003415(k)] is equal to A024451(n) = A003415(A002110(n)). For A024451(1) = 1, there is an infinite number of integers k for which A003415(k) = 1 (namely, all the primes), therefore the rows start from index n=2, with each having A377993(n) terms. Note that as a whole, this sequence is not monotonic, for example, the last term on row 9, 1171314743479 is larger than the first term of row 10, 6469693230.
Because A024451 is a subsequence of A048103, this is also. And if all terms of A024451 are squarefree as is conjectured, then all terms of this sequence are cubefree (A004709).

Examples

			The initial rows of the triangle:
Row n  terms
   2   6;
   3   30, 58;
   4   210, 435, 507;
   5   2310, 8435, 21827, 29233;
   6   30030, 39030, 62762, 69914, 76442, 78874;
   7   510510, 1342785, 1958673;
   8   9699690, 28235362;
   9   223092870, 975351895, 1527890095, ..., , 1167539981207, 1171314743479; (row 9 has 330 terms that are given separately in A378209)
  10   6469693230, 27623935255, 37262208055;
  11   200560490130, 345634019382, 440192669882;
  etc.
The only terms that occur on row 4 are k = 210, 435, 507 ( = 2*3*5*7, 3*5*29, 3 * 13^2) as they are only numbers for which A003415(k) = 247 = A024451(4) = A003415(A002110(4)), as we have (2*3*5*7)' = (3*5)'*(2*7) + (2*7)'*3*5 = (8*14) + (9*15) = (3*5*29)' = (3*5)'*29 + (3*5)*29' = (8*29 + 15*1) = (3 * 13 * 13)' = (3*13)'*13 + (3*13)*13' = 16*13 + 3*13*1 = 19*13 = 247.
 Note that 507 is so far the only known term in this triangle that is not squarefree (in A005117).
		

Crossrefs

Cf. A003415, A005117, A024451, A377993 (row lengths).
Subsequence of A048103, conjectured also to be a subsequence of A004709.
Cf. A002110 (left edge, from its term a(2)=6 onward), A378209 (row 9).

A378209 Antiderivatives of 334406399, numbers k for which A003415(k) = A024451(9) = A003415(A002110(9)).

Original entry on oeis.org

223092870, 975351895, 1527890095, 1885679383, 2189118743, 2329696457, 2338611863, 3485765789, 4586671213, 5453593183, 5472849253, 5674340053, 8071055747, 8931775397, 9332889127, 9453996491, 9601098443, 10293819917, 12717530039, 17343441881, 18636581773, 19498393573, 20167656703, 23244839627, 23515890737, 23556538969
Offset: 1

Views

Author

Antti Karttunen, Nov 20 2024

Keywords

Comments

Apart from the initial term A002110(9), all other terms are products of three distinct odd primes, A046389. Compare to the comments in A369239.
Note that A024451(9) = 334406399 = 43 * 163 * 47711 == -1 (mod 12). Compare the sequences A369450, A369451 and A369452 to see why there is such a sudden peak in A377993 at n=9, when compared to the nearby terms before and after.
For all n=1..330, A327969(a(n)) <= 7 = A099307(a(n)), because, when we apply A003415 successively, we get: A003415(334406399) -> 9835475 [= A369651(9)] -> 4893565 -> 978718 -> 564671 (which is a prime) -> 1 -> 0.

Crossrefs

Row 9 of irregular triangle A377992.
Subsequence of A099308, and after the initial term, subsequence of A046389.
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