A048720 -id:A048720 - cp's OEIS frontend

A325559 Numbers n such that for any divisor d of n, and some integer k, A048720(d,k) = n only for trivial cases d=1 and d=n.

2, 3, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 53, 55, 59, 61, 67, 69, 71, 73, 77, 79, 81, 83, 87, 89, 91, 97, 101, 103, 107, 109, 113, 115, 117, 121, 127, 131, 137, 139, 143, 145, 149, 151, 157, 163, 167, 169, 171, 173, 179, 181, 185, 191, 193, 197, 199, 203, 205, 209, 211, 213, 223, 227, 229, 233

Offset: 1

Antti Karttunen, May 11 2019

nonn

These are numbers n such that there are only two divisor pairs (d, n/d) [namely, the trivial pairs (1, n) and (n, 1)] that satisfy the condition that when their binary expansions are converted to (0,1)-polynomials (e.g., 13=1101[2] encodes X^3 + X^2 + 1), then their product is the (0,1)-polynomial similarly converted from n, when the multiplication is done over field GF(2).

Differs from A206074 for the first time at n=173, where a(173) = 555, a value missing from A206074, while the first three terms of A206074 not present in this sequence are k = 689, 781 and 913, for all of which A325560(k) = 3, not 2.

Antti Karttunen, Table of n, a(n) for n = 1..25000
Index entries for sequences related to polynomials in ring GF(2)[X]

Cf. A048720, A206074.
Positions of 2's in A325560, positions of 1's in A325563 (after the initial 1), fixed points of A325643 (after the initial 1).
Some subsequences: A257688 (after its initial 1), A325386 (the remaining terms).

A325560(n) = { my(p = Pol(binary(n))*Mod(1, 2)); sumdiv(n,d,my(q = Pol(binary(d))*Mod(1, 2)); !(p%q)); };
isA325559(n) = (2 == A325560(n));

A325563 a(1) = 1; for n > 1, a(n) is the largest proper divisor d of n such that A048720(d,k) = n for some k.

Original entry on oeis.org

1, 1, 1, 2, 1, 3, 1, 4, 3, 5, 1, 6, 1, 7, 5, 8, 1, 9, 1, 10, 7, 11, 1, 12, 1, 13, 9, 14, 1, 15, 1, 16, 3, 17, 7, 18, 1, 19, 3, 20, 1, 21, 1, 22, 15, 23, 1, 24, 7, 25, 17, 26, 1, 27, 1, 28, 3, 29, 1, 30, 1, 31, 21, 32, 5, 33, 1, 34, 1, 35, 1, 36, 1, 37, 15, 38, 1, 39, 1, 40, 1, 41, 1, 42, 17, 43, 1, 44, 1, 45, 1, 46, 31, 47, 19, 48, 1, 49, 33, 50

Offset: 1

Antti Karttunen, May 11 2019

nonn

For n > 1, a(n) is the largest proper divisor d of n for which it holds that when the binary expansion of d is converted to a (0,1)-polynomial (e.g., 13=1101[2] encodes X^3 + X^2 + 1), then that polynomial is a divisor of (0,1)-polynomial similarly converted from n, when the polynomial division is done over field GF(2). See the example.

			For n = 39 = 3*13, A032742(39) = 13, but 13 is not the answer because X^3 + X^2 + 1 does not divide X^5 + X^2 + X + 1 (39 is "100111" in binary) over GF(2). However, the next smaller divisor 3 works because X^5 + X^2 + X + 1 = (X^1 + 1)(X^4 + X^3 + X^2 + 1) when multiplication is done over GF(2). Note that 39 = A048720(3,29), where 29 is "11101" in binary. Thus a(39) = 3.

Antti Karttunen, Table of n, a(n) for n = 1..16384
Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537
Index entries for sequences related to polynomials in ring GF(2)[X]

Cf. A032742, A048720, A325560, A325564, A325567, A325643.

Cf. A325559 (positions of ones, after the initial 1).

A325563(n) = if(1==n,n, my(p = Pol(binary(n))*Mod(1, 2)); fordiv(n,d,if((d>1),my(q = Pol(binary(n/d))*Mod(1, 2)); if(0==(p%q), return(n/d)))));

A048720(b,c) = fromdigits(Vec(Pol(binary(b))*Pol(binary(c)))%2, 2);
A325563(n) = if(1==n,n,fordiv(n,d,if((d>1),for(t=1,n,if(A048720(n/d,t)==n,return(n/d)))))); \\ (Slow)

For all n, a(n) <= A032742(n).

A379121 Odd squares k for which A379113(k) > 1, i.e., k that have a proper unitary divisor d > 1 such that A048720(A065621(sigma(d)),sigma(k/d)) is equal to sigma(k).

Original entry on oeis.org

225, 3025, 3249, 12321, 29241, 38025, 91809, 216225, 247009, 354025, 408321, 751689, 772641, 855625, 919681, 1366561, 1595169, 3814209, 9828225, 11189025, 12173121, 12709225, 29430625, 47927929, 52403121, 66471409, 67486225, 77457601, 80263681, 94148209, 100661089, 110397049, 126540001, 204232681, 264875625, 328878225

Offset: 1

Antti Karttunen, Dec 18 2024

nonn

Of the first 2025 terms, only two, a(520) and a(1087) have multiple solutions. See the examples.

A284270 Square array A(r,c) = A048720(A065621(r), c) mod r, read by descending antidiagonals as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), etc.

Original entry on oeis.org

0, 0, 0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 0, 0, 3, 0, 0, 1, 0, 1, 2, 0, 0, 0, 0, 3, 4, 4, 0, 0, 0, 0, 2, 0, 1, 0, 0, 0, 0, 0, 2, 2, 1, 0, 7, 0, 0, 2, 0, 1, 0, 2, 0, 5, 6, 0, 0, 0, 0, 0, 0, 4, 0, 7, 2, 9, 0, 0, 0, 0, 4, 0, 2, 0, 1, 6, 7, 4, 0, 0, 1, 0, 1, 4, 0, 0, 8, 4, 0, 8, 8, 0, 0, 0, 0, 4, 0, 4, 0, 5, 4, 3, 0, 3, 8, 0, 0, 2, 0, 2, 0, 6, 0, 7, 2, 0, 4, 11, 2, 4

Offset: 1

Antti Karttunen, Apr 10 2017

			The top left 17 x 19 corner of the array:
   0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
   0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
   1,  2,  0,  1,  0,  0,  0,  2,  0,  0,  1,  0,  2,  0,  0,  1,  2
   0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
   3,  1,  3,  2,  2,  1,  0,  4,  1,  4,  2,  2,  1,  0,  0,  3,  1
   2,  4,  0,  2,  0,  0,  0,  4,  0,  0,  2,  0,  4,  0,  0,  2,  4
   4,  1,  1,  2,  4,  2,  0,  4,  6,  1,  6,  4,  1,  0,  0,  1,  5
   0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
   7,  5,  7,  1,  8,  5,  7,  2,  2,  7,  2,  1,  1,  5,  0,  4,  6
   6,  2,  6,  4,  4,  2,  0,  8,  2,  8,  4,  4,  2,  0,  0,  6,  2
   9,  7,  0,  3,  0,  0,  5,  6,  0,  0,  8,  0,  1, 10,  0,  1,  0
   4,  8,  0,  4,  0,  0,  0,  8,  0,  0,  4,  0,  8,  0,  0,  4,  8
   8,  3, 11,  6,  0,  9,  3, 12,  7,  0,  8,  5, 12,  6,  0, 11,  0
   8,  2,  2,  4,  8,  4,  0,  8, 12,  2, 12,  8,  2,  0,  0,  2, 10
   4,  8,  8,  1,  5,  1,  1,  2,  4, 10,  8,  2,  4,  2,  0,  4,  6
   0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0
  15, 13, 15,  9,  7, 13, 15,  1, 16, 14, 16,  9,  7, 13, 15,  2,  2
  14, 10, 14,  2, 16, 10, 14,  4,  4, 14,  4,  2,  2, 10,  0,  8, 12
  17, 15, 13, 11,  7,  7,  0,  3,  0, 14,  6, 14, 16,  0, 13,  6,  3

Cf. A048720, A065621, A115872, A277320, A284269 (transpose), A284273 (main diagonal), A284552 (column 1).

Row 3: A284557.

(define (A284270 n) (A284270bi (A002260 n) (A004736 n)))
(define (A284270bi row col) (modulo (A277320bi row col) row)) ;; For A277320bi, see in A277320.

A(r,c) = A277320(r,c) mod r = A048720(A065621(r), c) mod r.

A325570 Numbers n that have no divisor d > 1 such that A048720(A065621(d),n/d) = n.

Original entry on oeis.org

1, 3, 5, 7, 11, 13, 15, 17, 19, 23, 25, 27, 29, 31, 37, 39, 41, 43, 47, 51, 53, 55, 57, 59, 61, 63, 67, 69, 71, 73, 77, 79, 81, 83, 85, 87, 89, 91, 95, 97, 99, 101, 103, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 131, 137, 139, 141, 143, 145, 147, 149, 151, 157, 159, 163, 167, 169, 171, 173, 175, 177, 179, 181

Offset: 1

Antti Karttunen, May 10 2019

nonn

Antti Karttunen, Table of n, a(n) for n = 1..10000

Cf. A048720, A065621, A115872, A115873.
Positions of ones in A325565 and A325566.
Cf. A065091 (a subsequence), A325571 (the composite terms), A325572 (complement).
Subsequence of A005408 (odd numbers).

A048720(b,c) = fromdigits(Vec(Pol(binary(b))*Pol(binary(c)))%2, 2);
A065621(n) = bitxor(n-1,n+n-1);
isA325570(n) = fordiv(n,d,if(A048720(A065621(n/d),d)==n,return(d==n)));

A325643 a(1) = 1; for n > 1, a(n) is the least divisor d > 1 of n such that A048720(d,k) = n for some k.

Original entry on oeis.org

1, 2, 3, 2, 5, 2, 7, 2, 3, 2, 11, 2, 13, 2, 3, 2, 17, 2, 19, 2, 7, 2, 23, 2, 25, 2, 3, 2, 29, 2, 31, 2, 3, 2, 7, 2, 37, 2, 3, 2, 41, 2, 43, 2, 3, 2, 47, 2, 7, 2, 3, 2, 53, 2, 55, 2, 3, 2, 59, 2, 61, 2, 3, 2, 5, 2, 67, 2, 69, 2, 71, 2, 73, 2, 3, 2, 77, 2, 79, 2, 81, 2, 83, 2, 5, 2, 87, 2, 89, 2, 91, 2, 31, 2, 5, 2, 97, 2, 3, 2, 101, 2, 103, 2, 3

Offset: 1

Antti Karttunen, May 11 2019

nonn

For n > 1, a(n) is the least divisor d of n that is larger than 1 and for which it holds that when the binary expansion of d is converted to a (0,1)-polynomial (e.g., 13=1101[2] encodes X^3 + X^2 + 1), then that polynomial is a divisor of (0,1)-polynomial similarly converted from n, when the division is done over GF(2). See the example.

			For n = 21 = 3*7, 3 is not the answer because X^1 + 1 does not divide X^4 + X^2 + 1 (21 is "10101" in binary) over GF(2). However, the next larger divisor 7 works because X^4 + X^2 + 1 = (X^2 + X^1 + 1)^2 when multiplication is done over GF(2) (note that A048720(7,7) = 21). Thus a(21) = 7.

Antti Karttunen, Table of n, a(n) for n = 1..16384
Index entries for sequences related to polynomials in ring GF(2)[X]

Cf. A048720, A325559 (fixed points after 1), A325563, A325641, A325642.

A325643(n) = if(1==n,n, my(p = Pol(binary(n))*Mod(1, 2)); fordiv(n,d,if((d>1),my(q = Pol(binary(d))*Mod(1, 2)); if(0==(p%q), return(d)))));

a(2n) = 2.
For all n >= 1, a(A325559(n)) = A325559(n).
For all n >= 1, n = a(n) * A325641(n) = A048720(a(n), A325642(n)).

A379114 Numbers k for which A379113(k) > 1, i.e., k that have a proper unitary divisor d > 1 such that A048720(A065621(sigma(d)),sigma(k/d)) is equal to sigma(k).

Original entry on oeis.org

6, 10, 12, 14, 15, 20, 21, 22, 24, 26, 28, 30, 33, 35, 39, 40, 42, 44, 46, 48, 50, 51, 52, 55, 56, 57, 58, 60, 62, 63, 65, 66, 69, 70, 72, 75, 76, 77, 78, 80, 84, 86, 87, 88, 91, 92, 93, 94, 96, 100, 102, 104, 105, 108, 111, 112, 114, 115, 116, 118, 119, 120, 122, 123, 124, 126, 129, 132, 133, 136, 138, 140, 141, 143, 144

Offset: 1

Antti Karttunen, Dec 17 2024

nonn

Positions of terms > 1 in A379113.
Cf. A000396 (subsequence, at least the even terms are), A379118 (characteristic function).
Cf. also A325638, A325639 (not subsequences).

PARI
```
is_A379114(n) = (A379113(n)>1);
```

A115770 Integers i such that 7*i = A048720bi(11, i), where A048720bi implements the dyadic function given in A048720 (see A001317).

Original entry on oeis.org

0, 7, 14, 15, 28, 30, 31, 56, 60, 62, 63, 112, 120, 124, 126, 127, 224, 240, 248, 252, 254, 255, 448, 455, 480, 496, 504, 508, 510, 511, 896, 903, 910, 911, 960, 967, 992, 1008, 1016, 1020, 1022, 1023, 1792, 1799, 1806, 1807, 1820, 1822, 1823, 1920

Offset: 0

Antti Karttunen, Jan 30 2006

nonn

Here * stands for ordinary multiplication and A048720 is the carryless (GF(2)[X]) multiplication.

Index entries for sequences defined by congruent products between domains N and GF(2)[X]

Row 7 of A115872 (conjecture: also row 5).
Cf. A001317, A048717, A048720, A115767, A115772, A115774, A115776.
A115771 shows this sequence in binary.

A277825 a(n) = A048725(A065621(n)) = A048720(A065621(n),5).

Original entry on oeis.org

5, 10, 27, 20, 57, 54, 39, 40, 125, 114, 99, 108, 65, 78, 95, 80, 245, 250, 235, 228, 201, 198, 215, 216, 141, 130, 147, 156, 177, 190, 175, 160, 485, 490, 507, 500, 473, 470, 455, 456, 413, 402, 387, 396, 417, 430, 447, 432, 277, 282, 267, 260, 297, 294, 311, 312, 365, 354, 371, 380, 337, 350, 335, 320, 965, 970, 987, 980, 1017, 1014, 999, 1000

Offset: 1

Antti Karttunen, Nov 02 2016

Antti Karttunen, Table of n, a(n) for n = 1..8192
Index entries for sequences related to binary expansion of n

Column 3 of A277820, Column 5 of A277320.

Cf. A048720, A048724, A048725, A065621, A277823.

def A277825(n): return (m:=n^ (n&~-n)<<1)^m<<2 # Chai Wah Wu, Jun 29 2022

(define (A277825 n) (A048724 (A277823 n)))
(define (A277825 n) (A048720bi (A065621 n) 5)) ;; For A048720bi see the Scheme-program attachment in A048720.

a(n) = A048724(A277823(n)) = A048725(A065621(n)).

a(n) = A048720(A065621(n),5).

A284579 Carryless base-2 product (A048720) of run lengths in binary representation of n.

Original entry on oeis.org

1, 1, 1, 2, 2, 1, 2, 3, 3, 2, 1, 2, 4, 2, 3, 4, 4, 3, 2, 4, 2, 1, 2, 3, 6, 4, 2, 4, 6, 3, 4, 5, 5, 4, 3, 6, 4, 2, 4, 6, 3, 2, 1, 2, 4, 2, 3, 4, 8, 6, 4, 8, 4, 2, 4, 6, 5, 6, 3, 6, 8, 4, 5, 6, 6, 5, 4, 8, 6, 3, 6, 5, 6, 4, 2, 4, 8, 4, 6, 8, 4, 3, 2, 4, 2, 1, 2, 3, 6, 4, 2, 4, 6, 3, 4, 5, 10, 8, 6, 12, 8, 4, 8, 12, 6, 4, 2, 4, 8, 4, 6, 8, 12, 5, 6, 12, 6, 3, 6

Offset: 0

Antti Karttunen, Apr 14 2017

			For n=56, A007088(56) = "111000" in binary, we do carryless multiplication (in base-2) of 3 and 3, thus a(56) = A048720(3,3) = 5.

Antti Karttunen, Table of n, a(n) for n = 0..10922
Index entries for sequences related to binary expansion of n

Cf. A000975 (positions of ones).
Cf. A007088, A048720, A284580, A284581.
Differs from A167489 for the first time at n=56, where a(56) = 5, while A167489(56) = 9.

(define (A284579 n) (reduce A048720bi 1 (binexp->runcount1list n))) ;; Where A048720bi is a two-argument function implementing carryless binary product, A048720. For binexp->runcount1list see A167489.

A284581(n) = n - a(n).

cp's OEIS Frontend

A325559 Numbers n such that for any divisor d of n, and some integer k, A048720(d,k) = n only for trivial cases d=1 and d=n.

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A325563 a(1) = 1; for n > 1, a(n) is the largest proper divisor d of n such that A048720(d,k) = n for some k.

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A379121 Odd squares k for which A379113(k) > 1, i.e., k that have a proper unitary divisor d > 1 such that A048720(A065621(sigma(d)),sigma(k/d)) is equal to sigma(k).

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A284270 Square array A(r,c) = A048720(A065621(r), c) mod r, read by descending antidiagonals as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), etc.

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A325570 Numbers n that have no divisor d > 1 such that A048720(A065621(d),n/d) = n.

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A325643 a(1) = 1; for n > 1, a(n) is the least divisor d > 1 of n such that A048720(d,k) = n for some k.

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A379114 Numbers k for which A379113(k) > 1, i.e., k that have a proper unitary divisor d > 1 such that A048720(A065621(sigma(d)),sigma(k/d)) is equal to sigma(k).

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A115770 Integers i such that 7*i = A048720bi(11, i), where A048720bi implements the dyadic function given in A048720 (see A001317).

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A277825 a(n) = A048725(A065621(n)) = A048720(A065621(n),5).

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