A004771 -id:A004771 - cp's OEIS frontend

A157330 a(n) = 64*n - 8.

56, 120, 184, 248, 312, 376, 440, 504, 568, 632, 696, 760, 824, 888, 952, 1016, 1080, 1144, 1208, 1272, 1336, 1400, 1464, 1528, 1592, 1656, 1720, 1784, 1848, 1912, 1976, 2040, 2104, 2168, 2232, 2296, 2360, 2424, 2488, 2552, 2616, 2680, 2744, 2808, 2872, 2936, 3000

Offset: 1

Vincenzo Librandi, Feb 27 2009

The identity (128*n^2 - 32*n + 1)^2 - (4*n^2 - n)*(64*n - 8)^2 = 1 can be written as A157331(n)^2 - A033991(n)*a(n)^2 = 1. This is the case s=2 of the identity (8*n^2*s^4 - 8*n*s^2 + 1)^2 - (n^2*s^2 - n)*(8*n*s^3 - 4*s)^2 = 1. - Vincenzo Librandi, Jan 29 2012

Vincenzo Librandi, Table of n, a(n) for n = 1..10000
Vincenzo Librandi, X^2-AY^2=1.
Index entries for linear recurrences with constant coefficients, signature (2,-1).

Cf. A004771, A033991, A157331.

I:=[56, 120]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]]; // Vincenzo Librandi, Jan 29 2012

LinearRecurrence[{2,-1},{56,120},50] (* Vincenzo Librandi, Jan 29 2012 *)
64 Range[50]-8 (* Harvey P. Dale, Dec 31 2024 *)

for(n=1, 40, print1(64*n - 8", ")); \\ Vincenzo Librandi, Jan 29 2012

From Vincenzo Librandi, Jan 29 2012: (Start)
a(n) = 2*a(n-1) - a(n-2).
G.f.: x*(8*x+56)/(x-1)^2. (End)
a(n) = 8*A004771(n-1). - Michel Marcus, Aug 19 2018
E.g.f.: 8*(exp(x)*(8*x - 1) + 1). - Elmo R. Oliveira, Apr 04 2025

A214863 Numbers n such that n XOR 11 = n - 11.

Original entry on oeis.org

11, 15, 27, 31, 43, 47, 59, 63, 75, 79, 91, 95, 107, 111, 123, 127, 139, 143, 155, 159, 171, 175, 187, 191, 203, 207, 219, 223, 235, 239, 251, 255, 267, 271, 283, 287, 299, 303, 315, 319, 331, 335, 347, 351, 363

Offset: 1

Brad Clardy, Mar 09 2013

Links to sequences of the form n XOR m = n - m are found below with the value of m specified.

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Cf. A005408 (m=1), A042964 (m=2), A131098 (m=3), A047566 (m=4), A047550 (m=5), A047589 (m=6), A004771 (m=7), A115419 (m=8), A214865 (m=9), A214864 (m=10), A133894 (m=12), A125169 (m=15).

Cf. also A016825, A168392.

XOR := func;
m:=11;
for n in [1 .. 500] do
      if (XOR(n, m) eq n-m) then n; end if;
end for;

Select[Range[400],BitXor[#,11]==#-11&] (* or *) LinearRecurrence[{1,1,-1},{11,15,27},50] (* Harvey P. Dale, Jun 05 2021 *)

a(n)= 1+8*n-2*(-1)^n.
a(n)=A016825(n) + A168392(n) +  for n>0.
G.f. x*(11+4*x+x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Mar 10 2013

A317510 Numbers (4p+1)/3 where p is a Sophie Germain prime p > 3.

Original entry on oeis.org

7, 15, 31, 39, 55, 71, 111, 119, 151, 175, 231, 239, 255, 311, 319, 335, 375, 391, 479, 559, 575, 591, 655, 679, 791, 855, 871, 879, 911, 959, 991, 1015, 1079, 1215, 1271, 1351, 1359, 1375, 1399, 1471, 1631, 1639, 1719, 1879, 1919, 1935, 1975, 1999, 2015, 2079, 2111, 2135, 2311, 2415, 2519, 2535, 2575, 2631

Offset: 1

Hilko Koning, Jul 30 2018

nonn

It appears that this is a subsequence of A179882.
Define a set of consecutive positive odd numbers {1,......, (A077065(n)-1)} with n >= 3 and skip the number A077065(n)/2. Then the contraharmonic mean of that set gives the sequence. For example: ContraharmonicMean[{1, 3, 7, 9}] = 7, ContraharmonicMean[{1, 3, 5, 7, 9, 13, 15, 17, 19, 21}] = 15, ContraharmonicMean[{1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 25, 27, 29, 31, 33, 35, 37,39, 41, 43, 45}] = 31. - Hilko Koning, Aug 28 2018
Let p be a Sophie Germain prime and define h = 2p + 1 a safe prime. Then the contraharmonic mean of the totatives of h is given by: CHM(h) =  (Sum_{1 <= k < h, gcd(k, h) = 1} k^2) / (Sum_{1 <= k < h, gcd(k, h) = 1} k). Since h is prime, all integers k = 1, 2, ... , h - 1 are coprime to h. Then, CHM(h) = ((h - 1) * h * (2h-1) / 6) / ((h - 1) * h  / 2). Thus CHM = (2h-1) / 3 = (4p+1) / 3. These values are integers precisely when p == 2 mod 3, which holds for all Sophie Germain primes, p >= 5. The resulting values for the sequence A317510, which is therefore a subsequence of A179882. - Hilko Koning, Jun 17 2025

Muniru A Asiru, Table of n, a(n) for n = 1..5000

Cf. A005384, A179882.

Subsequence of A004767, and of A004771.

a:=[];; for p in [3..2000] do if IsPrime(p) and IsPrime(2*p+1) then Add(a,(4*p+1)/3); fi; od; a; # Muniru A Asiru, Aug 28 2018

lst = {}; Do[If[PrimeQ[p] && PrimeQ[2 p + 1], AppendTo[lst, (4 p + 1)/3]], {p, 5, 2*10^3}]; lst
4 (Select[Prime@Range[3, 300], PrimeQ[2 # + 1] &] + 1)/3 - 1 (* Robert G. Wilson v, Jul 30 2018 *)

lista(nn) = {forprime (p=5, nn, if (isprime(2*p+1), print1((4*p+1)/3, ", ")););} \\ Michel Marcus, Aug 27 2018

A047589 Numbers that are congruent to {6, 7} mod 8.

Original entry on oeis.org

6, 7, 14, 15, 22, 23, 30, 31, 38, 39, 46, 47, 54, 55, 62, 63, 70, 71, 78, 79, 86, 87, 94, 95, 102, 103, 110, 111, 118, 119, 126, 127, 134, 135, 142, 143, 150, 151, 158, 159, 166, 167, 174, 175, 182, 183, 190, 191, 198, 199, 206, 207, 214, 215, 222, 223, 230, 231

Offset: 1

N. J. A. Sloane

These are the values of n for which binomial(n,6) is odd. See Maple code. - Gary Detlefs, Nov 29 2011

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

Union of A017137 and A004771.

Cf. A047451, A047521.

for i from 1 to 240 do if(floor((i mod 8)/6) <>0) then print(i) fi od; # Gary Detlefs, Nov 30 2011

LinearRecurrence[{1,1,-1},{6,7,14},60] (* Harvey P. Dale, Sep 11 2017 *)

a(n) = 8*n-a(n-1)-3 with n>1, a(1)=6. - Vincenzo Librandi, Aug 06 2010
a(n) = 6*floor((n-1)/2) + n + 5. - Gary Detlefs, Nov 29 2011
a(n) = a(n-1)+a(n-2)-a(n-3). G.f.: x*(6+x+x^2)/((1-x)^2*(1+x)). - Colin Barker, Mar 18 2012
a(n) = (1-3*(-1)^n+8*n)/2. - Colin Barker, May 14 2012
Sum_{n>=1} (-1)^(n+1)/a(n) = sqrt(2)*Pi/16 - log(2)/8 - sqrt(2)*log(sqrt(2)+1)/8. - Amiram Eldar, Dec 18 2021

A137196 Lucky numbers (A000959) which are congruent to 7 mod 8.

Original entry on oeis.org

7, 15, 31, 63, 79, 87, 111, 127, 135, 151, 159, 223, 231, 303, 319, 327, 367, 391, 399, 415, 463, 487, 495, 511, 519, 535, 559, 583, 591, 615, 631, 639, 655, 679, 727, 735, 823, 831, 855, 895, 903, 927, 975, 991, 1023, 1039, 1087, 1095, 1167, 1183, 1231, 1263, 1303, 1455

Offset: 1

N. J. A. Sloane, Mar 07 2008

nonn

Amiram Eldar, Table of n, a(n) for n = 1..10000

Intersection of A000959 and A004771.

A144204 Array A(k,n) = (n+k-2)*(n-1) - 1 (k >= 1, n >= 1) read by antidiagonals.

Original entry on oeis.org

-1, -1, 0, -1, 1, 3, -1, 2, 5, 8, -1, 3, 7, 11, 15, -1, 4, 9, 14, 19, 24, -1, 5, 11, 17, 23, 29, 35, -1, 6, 13, 20, 27, 34, 41, 48, -1, 7, 15, 23, 31, 39, 47, 55, 63, -1, 8, 17, 26, 35, 44, 53, 62, 71, 80, -1, 9, 19, 29, 39, 49, 59, 69, 79, 89, 99, -1, 10, 21, 32, 43, 54, 65, 76, 87

Offset: 1

Jonathan Vos Post, Sep 13 2008

Arises in complete intersection threefolds,
Also can be produced as a triangle read by rows: a(n, k) = nk - (n + k). - Alonso del Arte, Jul 09 2009
Kosta: Let X be a complete intersection of two hypersurfaces F_n and F_k in the projective space P^5 of degree n and k respectively. with n=>k, such that the singularities of X are nodal and F_k is smooth. We prove that if the threefold X has at most (n+k-2)*(n-1) - 1 singular points, then it is factorial.

			From _R. J. Mathar_, Jul 10 2009: (Start)
The rows A(n,1), A(n,2), A(n,3), etc., are :
.-1...0...3...8..15..24..35..48..63..80..99.120.143.168 A067998
.-1...1...5..11..19..29..41..55..71..89.109.131.155.181 A028387
.-1...2...7..14..23..34..47..62..79..98.119.142.167.194 A008865
.-1...3...9..17..27..39..53..69..87.107.129.153.179.207 A014209
.-1...4..11..20..31..44..59..76..95.116.139.164.191.220 A028875
.-1...5..13..23..35..49..65..83.103.125.149.175.203.233 A108195
.-1...6..15..26..39..54..71..90.111.134.159.186.215.246
.-1...7..17..29..43..59..77..97.119.143.169.197.227.259
.-1...8..19..32..47..64..83.104.127.152.179.208.239.272
.-1...9..21..35..51..69..89.111.135.161.189.219.251.285
.-1..10..23..38..55..74..95.118.143.170.199.230.263.298
.-1..11..25..41..59..79.101.125.151.179.209.241.275.311
.-1..12..27..44..63..84.107.132.159.188.219.252.287.324
.-1..13..29..47..67..89.113.139.167.197.229.263.299.337 Cf. A126719.
(End)
As a triangle:
. 0
. 1, 3
. 2, 5, 8
. 3, 7, 11, 15
. 4, 9, 14, 19, 24
. 5, 11, 17, 23, 29, 35
. 6, 13, 20, 27, 34, 41, 48
. 7, 15, 23, 31, 39, 47, 55, 63
. 8, 17, 26, 35, 44, 53, 62, 71, 80

Dimitra Kosta, Factoriality of complete intersection threefolds arXiv:0808.4071 [math.AG]

Row 1 = A067998(n) for n>0. Row 2 = A028387(n) for n>0.Column 1 = -A000012(n). Column 2 = A001477. Column 3 = A005408(k). Column 4 = A016789(k+1). Column 5 = A004767(k+2). Column 6 = A016897(k+3). Column 7 = A016969(k+4). Column 8 = A017053(k+5). Column 9 = A004771(k+6). Column 10 = A017257(k+7).

Cf. A000012, A001477, A004767, A004771, A005408, A016789, A016897, A016969, A017053, A028387, A067998, A126719.

A := proc(k,n) (n+k-2)*(n-1)-1 ; end: for d from 1 to 13 do for n from 1 to d do printf("%d,",A(d-n+1,n)) ; od: od: # R. J. Mathar, Jul 10 2009

a[n_, k_] := a[n, k] = n*k - (n + k); ColumnForm[Table[a[n, k], {n, 10}, {k, n}], Center] (* Alonso del Arte, Jul 09 2009 *)

A[k,n] = (n+k-2)*(n-1) - 1.

Antidiagonal sum: Sum_{n=1..d} A(d-n+1,n) = d*(d^2-2d-1)/2 = -A110427(d). - R. J. Mathar, Jul 10 2009

Duplicate of 6th antidiagonal removed by R. J. Mathar, Jul 10 2009
Keyword:tabl added by R. J. Mathar, Jul 23 2009
Edited by N. J. A. Sloane, Sep 14 2009. There was a comment that the defining formula was wrong, but it is perfectly correct.

A268063 Primes of the form (k^3 - k^2 - k - 1)/2 for some integer k > 0.

Original entry on oeis.org

7, 47, 599, 1567, 5807, 7487, 9463, 20807, 24623, 28879, 33599, 81647, 111599, 123007, 161839, 225263, 262399, 282407, 397807, 541007, 573247, 606743, 641519, 922807, 1115399, 1513727, 1577383, 1709999, 1779007, 1849847, 1997119, 2399039, 2573807, 2948399

Offset: 1

Emre APARI, Jan 25 2016

Also primes of the form 4*k^3 + 4*k^2 - 1.

			k=15: (15^3 - 15^2 - 15 - 1)/2 = 1567 (is prime).

G. C. Greubel, Table of n, a(n) for n = 1..3240

Cf. A004771, A042991, A168489.

[a: n in [0..200] | IsPrime(a) where a is (n^3-n^2-n-1) div 2 ]; // Vincenzo Librandi, Jan 26 2016

Select[Table[(n^3 - n^2 - n - 1) / 2, {n, 200}], PrimeQ] (* Vincenzo Librandi, Jan 26 2016 *)

lista(nn) = for(n=1, nn, if(ispseudoprime(p=4*n^3+4*n^2-1), print1(p, ", "))); \\ Altug Alkan, Mar 14 2016

[(k^3-k^2-k-1)/2 for k in [2*i+1 for i in [1..100]] if is_prime(Integer((k^3-k^2-k-1)/2))] # Tom Edgar, Jan 25 2016

More terms from Tom Edgar, Jan 25 2016

A296579 Numbers that are not the sum of 3 squares and a nonnegative 9th power.

Original entry on oeis.org

112, 240, 368, 448, 496, 624, 752, 880, 960, 1008, 1136, 1264, 1392, 1472, 1520, 1648, 1776, 1904, 1984, 2032, 2160, 2288, 2416, 2496, 2544, 2672, 2800, 2928, 3008, 3056, 3184, 3312, 3440, 3520, 3568, 3696, 3824, 3952, 4032, 4080, 4208, 4336, 4464, 4544, 4592

Offset: 1

XU Pingya, Jan 30 2018

a(n) consists of the number of forms 16*(8i + 7) (0 <= i <= 152) and 64*(8j + 7) (0 <= j <= 37).

The last term in this sequence is a(191) = 19568 = 16*(8*152 + 7) (see A297970).

Wikipedia, Legendre's three-square theorem

Finite subsequence of A004215.
A297970 is a subsequence.
Cf. A004771, A022552, A022557, A022561, A022566, A111151.

t1=Table[4^2*(8j+7), {j,0,152}];
t2=Table[4^3*(8j+7), {j,0,37}];
t=Union[t1, t2]

A326354 a(n) is the number of fractions reduced to lowest terms with numerator and denominator less than or equal to n in absolute value.

Original entry on oeis.org

1, 3, 7, 15, 23, 39, 47, 71, 87, 111, 127, 167, 183, 231, 255, 287, 319, 383, 407, 479, 511, 559, 599, 687, 719, 799, 847, 919, 967, 1079, 1111, 1231, 1295, 1375, 1439, 1535, 1583, 1727, 1799, 1895, 1959, 2119, 2167, 2335, 2415, 2511, 2599, 2783, 2847, 3015, 3095

Offset: 0

Stefano Spezia, Jul 06 2019

nonn

All the terms of this sequence are odd numbers (A005408).
For n > 1, a(n) is congruent to 7 mod 8 (A004771).
Apart from a(0) the same as A171503. - R. J. Mathar, Sep 03 2019

			a(0) = 1 since X(0) = {0};
a(1) = 3 since X(1) = {-1, 0, 1};
a(2) = 7 since X(2) = {-2, -1, -1/2, 0, 1/2, 1, 2};
a(3) = 15 since X(3) = {-3, -2, -3/2, -1, -2/3, -1/2, -1/3, 0, 1/3, 1/2, 2/3, 1, 3/2, 2, 3};
...

Cf. A000010, A004771, A005408, A171503, A206350.

I:=[1, 3]; [n le 2 select I[n] else Self(n-1)+4*EulerPhi(n-1): n in [1..51]];

nmax = 50; a=vector(nmax+1); a[1]=1; a[2]=3; for(n=3, nmax+1, a[n]=a[n-1]+4*eulerphi(n-1)); a

a(0) = 1, a(1) = 3 and a(n) = a(n-1) + 4*A000010(n) for n > 1, where A000010(n) = phi(n).

a(n) = 2*A206350(n+1) - 1. - Michel Marcus, Jul 07 2019

A337218 The positive integers uniquely represented by the ternary form x^2 + 2y^2 + 2z^2, with integers x <= 0, and 0 <= y <= z.

Original entry on oeis.org

1, 2, 3, 5, 6, 10, 12, 13, 14, 21, 22, 30, 37, 42, 46, 48, 58, 70, 78, 93, 133, 142, 190, 192, 253, 768, 3072, 12288, 49152, 196608, 786432, 3145728, 12582912, 50331648, 201326592, 805306368, 3221225472, 12884901888

Offset: 1

Wolfdieter Lang, Aug 20 2020

This sequence gives Theorem 2.2. of Kaplansky, p. 88, with a proof on p. 90.
This sequence is composed of two finite ones and an infinite one: (i) 2*A337217 = {2, 6, 10, 14, 22, 30, 42, 46, 58, 70, 78, 142, 190}, the even members of A094739, (ii) {1, 5, 13, 21, 37, 93, 133, 253}, the 1 (mod 4) members of A094739, and (iii) A002001(k+1) = 4^k*3, for integer k >= 0. Beginning with a(26) = 768 only the powers 4^k*3, for k >= 4 appear.
See eq. (2.2), (2,4), p. 87, of Kaplansky for the two finite sequences with 13 and 8 members, respectively.
The positive integers which have no such solution (x, y, z) are given by 4^k*(7+8*m) = A002001(k+1)*A004771(m), for k >= 0 and m >= 0. See Kaplansky, p. 88. The other missing positive integers have more than 1 solution.

			4 is not a member because (x, y, z) = (0, 1, 1) and (2, 0, 0) give both 4.
3 is a member with one solution (1, 0, 1).
5 is a member with one solutuion (1, 1, 1).
7 is not a member because there is no solution.
11 is not a member because there are two solutions (1, 1, 2) and (3, 0, 1).

Irving Kaplansky, Integers Uniquely Represented by Certain Ternary Forms, in "The Mathematics of Paul Erdős I", Ronald. L. Graham and Jaroslav Nešetřil (Eds.), Springer, 1997, pp. 86 - 94.

Cf. A002001, A004771, A094739.

See the comment for the union of the three sequences (i), (ii) and (iii).

cp's OEIS Frontend

A157330 a(n) = 64*n - 8.

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A214863 Numbers n such that n XOR 11 = n - 11.

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A317510 Numbers (4p+1)/3 where p is a Sophie Germain prime p > 3.

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GAP

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A047589 Numbers that are congruent to {6, 7} mod 8.

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A137196 Lucky numbers (A000959) which are congruent to 7 mod 8.

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A144204 Array A(k,n) = (n+k-2)*(n-1) - 1 (k >= 1, n >= 1) read by antidiagonals.

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A268063 Primes of the form (k^3 - k^2 - k - 1)/2 for some integer k > 0.

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A296579 Numbers that are not the sum of 3 squares and a nonnegative 9th power.

A337218 The positive integers uniquely represented by the ternary form x^2 + 2y^2 + 2z^2, with integers x <= 0, and 0 <= y <= z.