A292939 -id:A292939 - cp's OEIS frontend

A292270 Sum of all partial fractions in the algorithm used for calculation of A002326(n).

1, 1, 4, 1, 13, 25, 36, 1, 38, 81, 12, 26, 124, 121, 196, 1, 103, 73, 324, 42, 224, 175, 91, 147, 232, 14, 676, 170, 303, 841, 900, 1, 264, 1089, 385, 364, 93, 301, 585, 563, 1093, 1681, 44, 355, 152, 118, 83, 484, 1254, 763, 2500, 1043, 156, 2809, 996, 564, 952, 931, 71, 387, 3325, 176, 3124, 1, 649, 4225, 554, 1081

Offset: 0

Vladimir Shevelev and Antti Karttunen, Oct 05 2017

nonn

This sequence gives important additional insight into the algorithm for the calculation of A002326 (see A179680 for its description). Let us estimate how many steps are required before (the first) 1 will appear. Note that all partial fractions (which are indeed, integers) are odd residues modulo 2*n+1 from the interval [1,2*n-1]. So, if there is no repetition, then the number of steps does not exceed n. Suppose then that there is a repetition before the appearance of 1. Then for an odd residue k from [1, 2*n-1], 2^m_1 == 2^m_2 == k (mod 2*n+1) such that m_2 > m_1. But then 2^(m_2-m_1) == 1 (mod 2*n+1). So, since m_2 - m_1 < m_2, it means that 1 should appear earlier than the repetition of k, which is a contradiction. So the number of steps <= n. For example, for n=9, 2*n+1 = 19, we have exactly 9 steps with all other odd residues <= 17 modulo 19 appearing before the final 1: 5, 3, 11, 15, 17, 9, 7, 13, 1.

A001122 gives the odd numbers k such that a((k-1)/2) = A000290((k-1)/2).

			Let n = 9. According to the comment, a(9) = 5 + 3 + 11 + 15 + 17 + 9 + 7 + 13 + 1 = 81.

Antti Karttunen, Table of n, a(n) for n = 0..10001

Cf. A000265, A000290, A001122, A001917, A002326, A006519, A163782, A179382, A179680, A292239, A292265, A292947, A293218, A293219.

Cf. A000225 (gives the positions of ones), A292938 (of squares), A292939 (and the corresponding odd numbers), A292940 (odd numbers corresponding to squares larger than one), A292379 (odd numbers corresponding to squares less than n^2).

A000265(n) = (n >> valuation(n, 2));
A006519(n) = 2^valuation(n, 2);
A292270(n) = { my(x = n+n+1, z = ((1+x)/A006519(1+x)), m = A000265(1+x)); while(m!=1, z += ((x+m)/A006519(x+m)); m = A000265(x+m)); z; };

(define (A292270 n) (let ((x (+ n n 1))) (let loop ((z (/ (+ 1 x) (A006519 (+ 1 x)))) (k 1)) (let ((m (A000265 (+ x k)))) (if (= 1 m) z (loop (+ z (/ (+ x m) (A006519 (+ x m)))) m))))))

For all n >= 1, A000196(a((A001122(1+n)-1)/2)) = (A001122(1+n)-1)/2, in other words, a(A163782(n)) = A000290(A163782(n)).

A292938 Numbers n for which A292270(n) is a square.

Original entry on oeis.org

0, 1, 2, 3, 5, 6, 7, 9, 13, 14, 15, 18, 26, 29, 30, 31, 33, 41, 47, 50, 53, 63, 65, 69, 74, 81, 86, 89, 90, 98, 105, 113, 127, 134, 138, 146, 152, 158, 173, 174, 186, 189, 194, 209, 210, 221, 230, 233, 245, 254, 255, 259, 261, 270, 273, 278, 281, 293, 306, 309, 326, 329, 330, 338, 350, 354, 378, 386, 393, 398, 410

Offset: 1

Antti Karttunen and Vladimir Shevelev, Oct 06 2017

nonn

Positions of ones in A293218.

Antti Karttunen, Table of n, a(n) for n = 1..1001

Cf. A292270, A292939 (corresponding odd numbers).

Cf. A000225 (a subsequence), A293218.

A292940 Odd numbers k for which A292270((k-1)/2) is a square larger than one.

Original entry on oeis.org

5, 11, 13, 19, 27, 29, 37, 53, 59, 61, 67, 83, 95, 101, 107, 131, 139, 149, 163, 173, 179, 181, 197, 211, 227, 269, 277, 293, 305, 317, 347, 349, 373, 379, 389, 419, 421, 443, 461, 467, 491, 509, 519, 523, 541, 547, 557, 563, 587, 613, 619, 653, 659, 661, 677, 701, 709, 757, 773, 787, 797, 821, 827, 829, 853

Offset: 1

Antti Karttunen and Vladimir Shevelev, Oct 06 2017

nonn

Antti Karttunen, Table of n, a(n) for n = 1..1001

Subsequence of A292939.
Cf. A001122 (a subsequence).
Cf. A292270.

A292379 Odd numbers k such that A292270((k-1)/2) is a square < ((k-1)/2)^2.

Original entry on oeis.org

7, 15, 27, 31, 63, 95, 127, 255, 277, 305, 511, 519, 1023, 1921, 2047, 2349, 3575, 4095, 8191, 8743, 10525, 16383, 17955, 24661, 26585, 27305, 32767, 36611, 40677, 65535, 85173, 95571, 122915, 131071, 262143, 360213, 386019, 524287, 667879, 736251, 806603, 1020963

Offset: 1

Antti Karttunen and Vladimir Shevelev, Oct 06 2017

nonn

Subsequence of A292939.
Doesn't contain any terms of A001122.
Cf. A000225 (subsequence from its term a(3) = 7 onward).
Cf. A292270.

A000265(n) = n >> valuation(n, 2);
A292270(n) = { my(x = n+n+1, m = A000265(1+x), z = m); while(m!=1, z += A000265(x+m); m = A000265(x+m)); z; };
n=1; k=0; while(k < 120, m = A292270(n); if(issquare(m) && (m < n^2), k++; write("b292379.txt", k, " ", 1+(2*n))); n++);

More terms from Jinyuan Wang, Apr 29 2025

cp's OEIS Frontend

A292270 Sum of all partial fractions in the algorithm used for calculation of A002326(n).

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A292938 Numbers n for which A292270(n) is a square.

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A292940 Odd numbers k for which A292270((k-1)/2) is a square larger than one.

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A292379 Odd numbers k such that A292270((k-1)/2) is a square < ((k-1)/2)^2.

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