A027688 -id:A027688 - cp's OEIS frontend

A171746 Let f(n) = n + floor(sqrt(n)). Then a(n) is the smallest number of iterations of f on n such that a perfect square is obtained.

3, 2, 1, 5, 2, 4, 1, 3, 7, 2, 4, 6, 1, 3, 5, 9, 2, 4, 6, 8, 1, 3, 5, 7, 11, 2, 4, 6, 8, 10, 1, 3, 5, 7, 9, 13, 2, 4, 6, 8, 10, 12, 1, 3, 5, 7, 9, 11, 15, 2, 4, 6, 8, 10, 12, 14, 1, 3, 5, 7, 9, 11, 13, 17, 2, 4, 6, 8, 10, 12, 14, 16, 1, 3, 5, 7, 9, 11, 13, 15, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 1, 3, 5

Offset: 1

Neven Juric (neven.juric(AT)apis-it.hr), Oct 07 2010

nonn

Iterate A028392, starting with n: a(n) is the number of steps until a square will be reached. - Reinhard Zumkeller, Feb 23 2012

			f(9)=12, f(12)=15, f(15)=18, f(18)=22, f(22)=26, f(26)=31, f(31)=36. The first square number in this sequence 12,15,18,22,26,31,36 is on the seventh place and therefore a(9)=7.

Matematicko-fizicki list 1/144, problem 2-2, page 29, (1985-1986).

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Cf. A010052, A028392.

a171746 = (+ 1) . length . takeWhile (== 0) .
                           map a010052 . tail . iterate a028392
-- Reinhard Zumkeller, Feb 23 2012, Oct 14 2010

f[n_] := Length@ NestWhileList[ # + Floor@Sqrt@# &, n, ! IntegerQ@Sqrt@# || # == n &] - 1; Array[f, 93] (* Robert G. Wilson v, Oct 08 2010 *)

f(n) = n + sqrtint(n); \\ A028392
a(n) = my(k=1); while (!issquare(n=f(n)), k++); k; \\ Michel Marcus, Nov 06 2022

From Robert G. Wilson v, Oct 08 2010: (Start)
a(k)=1 for A002061(n): n^2 - n + 1 for n>1;
a(k)=2 for A002522(n): n^2 + 1     for n>1;
a(k)=3 for A014206(n): n^2 + n + 2 for n>1;
a(k)=4 for A059100(n): n^2 + 2     for n>1;
a(k)=5 for A027688(n): n^2 + n + 3 for n>2;
a(k)=6 for A117950(n): n^2 + 3     for n>2;
a(k)=7 for A027689(n): n^2 + n + 4 for n>4;
a(k)=8 for A087475(n): n^2 + 4     for n>3;
a(k)=9 for A027690(n): n^2 + n + 5 for n>4; ... (End)
a(n^2) = 2*n + 1: a(A000290(n)) = A005408(n). - Reinhard Zumkeller, Oct 14 2010

A354902 a(n) = 2n^2 - 6n + 11 for n > 1 with a(0)=1 and a(1)=3.

Original entry on oeis.org

1, 3, 7, 11, 19, 31, 47, 67, 91, 119, 151, 187, 227, 271, 319, 371, 427, 487, 551, 619, 691, 767, 847, 931, 1019, 1111, 1207, 1307, 1411, 1519, 1631, 1747, 1867, 1991, 2119, 2251, 2387, 2527, 2671, 2819, 2971, 3127, 3287, 3451, 3619, 3791, 3967, 4147, 4331, 4519, 4711, 4907

Offset: 0

Sumukh Patel, Jun 11 2022

a(n) is the minimum number of nodes required for a full binary tree where each node in all longest paths from the root node down to any leaf node is height-balanced and the root node has a height balance factor of 0.

Full binary tree: A binary tree is called a full binary tree if each node has exactly two children or no children.

			The diagrams below illustrate the terms a(3)=11 and a(4)=19.
           R                         R
          / \                       / \
         /   \                     /   \
        /     \                   /     \
       o       o                 /       \
      / \     / \               /         \
     o   N   N   o             /           \
    / \         / \           /             \
   N   N       N   N         o               o
                            / \             / \
                           /   \           /   \
                          /     \         /     \
                         o       o       o       o
                        / \     / \     / \     / \
                       o   N   N   N   N   N   o   N
                      / \                     / \
                     N   N                   N   N

Michael De Vlieger, Table of n, a(n) for n = 0..10000
Lecture Notes for Computer Science 2530, Height-balanced trees
NIST, Root node
NIST, Leaf node
Wikipedia, Full binary tree
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

Cf. A022856, A027688.

int a(int n){ return n>1 ? 2*(n*n) - 6*n + 11 : 2*n + 1; }

CoefficientList[Series[(1 + x^2 - 2 x^3 + 4 x^4)/(1 - x)^3, {x, 0, 51}], x] (* Michael De Vlieger, Jun 19 2022 *)

a(n) = 2*A027688(n-2) + 1, for n >= 2.
a(n) = 4*A022856(n+2) - 1, for n >= 1.
a(n) = a(n-1) + 4*(n-2) for n >= 3.
G.f.: (1 + x^2 - 2*x^3 + 4*x^4)/(1 - x)^3. - Stefano Spezia, Jun 12 2022
Sum_{n>=2} 1/a(n) = Pi*tanh(sqrt(13)*Pi/2)/(2*sqrt(13)). - Amiram Eldar, Jul 10 2022

A214870 Natural numbers placed in table T(n,k) layer by layer. The order of placement: at the beginning filled odd places of layer clockwise, next - even places counterclockwise. T(n,k) read by antidiagonals.

Original entry on oeis.org

1, 2, 3, 5, 4, 7, 10, 9, 8, 13, 17, 16, 6, 14, 21, 26, 25, 11, 12, 22, 31, 37, 36, 18, 15, 20, 32, 43, 50, 49, 27, 24, 23, 30, 44, 57, 65, 64, 38, 35, 19, 33, 42, 58, 73, 82, 81, 51, 48, 28, 29, 45, 56, 74, 91, 101, 100, 66, 63, 39, 34, 41, 59, 72, 92, 111

Offset: 1

Boris Putievskiy, Mar 11 2013

Permutation of the natural numbers.
a(n) is a pairing function: a function that reversibly maps Z^{+} x Z^{+} onto Z^{+}, where Z^{+} is the set of integer positive numbers.
Layer is pair of sides of square from T(1,n) to T(n,n) and from T(n,n) to T(n,1).
Enumeration table T(n,k) layer by layer. The order of the list:
  T(1,1)=1;
  T(1,2), T(2,1), T(2,2);
  . . .
  T(1,n), T(3,n), ... T(n,3), T(n,1); T(n,2), T(n,4), ... T(4,n), T(2,n);
  . . .

			The start of the sequence as table:
   1   2   5  10  17  26 ...
   3   4   9  16  25  36 ...
   7   8   6  11  18  27 ...
  13  14  12  15  24  35 ...
  21  22  20  23  19  28 ...
  31  32  30  33  29  34 ...
  ...
The start of the sequence as triangle array read by rows:
   1;
   2,  3;
   5,  4,  7;
  10,  9,  8, 13;
  17, 16,  6, 14, 21;
  26, 25, 11, 12, 22, 31;
  ...

Boris Putievskiy, Rows n = 1..140 of triangle, flattened
Boris Putievskiy, Transformations [of] Integer Sequences And Pairing Functions arXiv:1212.2732 [math.CO], 2012.
Eric Weisstein's World of Mathematics, Pairing functions
Index entries for sequences that are permutations of the natural numbers

Cf. A060734, A060736, A185725, A213921, A213922; table T(n,k) contains: in rows A002522, A000290, A059100, A005563, A117950, A008865, A087475, A028872, A117951, A028347, A114949, A028875, A117619, A028878, A189833, A028881, A189834, A028884, A114948, A028560, A189836; in columns A002061, A014206, A002378, A027688, A028387, A027689, A028552, A027690, A014209, A027691, A027692, A082111, A027693, A028557, A027694, A108195, A187710, A048058, A048840.

t=int((math.sqrt(8*n-7) - 1)/ 2)
i=n-t*(t+1)/2
j=(t*t+3*t+4)/2-n
if i > j:
   result=i*i-i+(j%2)*(2-(j+1)/2)+((j+1)%2)*(j/2+1)
else:
   result=j*j-2*(i%2)*j + (i%2)*((i+1)/2+1) + ((i+1)%2)*(-i/2+1)

As table
T(n,k) = k*k-2*(n mod 2)*k+(n mod 2)*((n+1)/2+1)+((n+1) mod 2)*(-n/2+1), if n<=k;
T(n,k) = n*n-n+(k mod 2)*(2-(k+1)/2)+((k+1) mod 2)*(k/2+1), if n>k.
As linear sequence
a(n) = j*j-2*(i mod 2)*j+(i mod 2)*((i+1)/2+1)+((i+1) mod 2)*(-i/2+1), if i<=j;
a(n) = i*i-i+(j mod 2)*(2-(j+1)/2)+((j+1) mod 2)*(j/2+1), if i>j; where i=n-t*(t+1)/2, j=(t*t+3*t+4)/2-n, t=floor((-1+sqrt(8*n-7))/2).

A268101 Smallest prime p such that some polynomial of the form ax^2 - bx + p generates distinct primes in absolute value for x = 1 to n, where 0 < a < p and 0 <= b < p.

Original entry on oeis.org

2, 3, 5, 5, 7, 7, 11, 11, 11, 11, 13, 13, 17, 17, 17, 17, 19, 19, 23, 23, 23, 23, 29, 29, 29, 29, 29, 29, 31, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 647, 1277, 1979, 2753

Offset: 1

Arkadiusz Wesolowski, Jan 26 2016

			a(1) = 2 (a prime), x^2 + 2 gives a prime for x = 1.
a(2) = 3 (a prime), 2*x^2 + 3 gives distinct primes for x = 1 to 2.
a(4) = 5 (a prime), 2*x^2 + 5 gives distinct primes for x = 1 to 4.
a(6) = 7 (a prime), 4*x^2 + 7 gives distinct primes for x = 1 to 6.
a(10) = 11 (a prime), 2*x^2 + 11 gives distinct primes for x = 1 to 10.
a(12) = 13 (a prime), 6*x^2 + 13 gives distinct primes for x = 1 to 12.
a(16) = 17 (a prime), 6*x^2 + 17 gives distinct primes for x = 1 to 16.
a(18) = 19 (a prime), 10*x^2 + 19 gives distinct primes for x = 1 to 18.
a(22) = 23 (a prime), 3*x^2 - 3*x + 23 gives distinct primes for x = 1 to 22.
a(28) = 29 (a prime), 2*x^2 + 29 gives distinct primes for x = 1 to 28.
a(29) = 31 (a prime), 2*x^2 - 4*x + 31 gives distinct primes for x = 1 to 29.
a(40) = 41 (a prime), x^2 - x + 41 gives distinct primes for x = 1 to 40.
a(41) = 647 (a prime), abs(36*x^2 - 594*x + 647) gives distinct primes for x = 1 to 41.
a(42) = 1277 (a prime), abs(36*x^2 - 666*x + 1277) gives distinct primes for x = 1 to 42.
a(43) = 1979 (a prime), abs(36*x^2 - 738*x + 1979) gives distinct primes for x = 1 to 43.
a(44) = 2753 (a prime), abs(36*x^2 - 810*x + 2753) gives distinct primes for x = 1 to 44.

Carlos Rivera, Problem 12
Eric Weisstein's World of Mathematics, Prime-Generating Polynomial

Cf. A027688, A027753, A027690, A027755, A048058, A048059, A007635, A007639, A007637, A007641, A202018, A005846, A117081, A050268, A268109.

A055630 Table T(k,m) = k^2 + m read by antidiagonals.

Original entry on oeis.org

0, 1, 1, 4, 2, 2, 9, 5, 3, 3, 16, 10, 6, 4, 4, 25, 17, 11, 7, 5, 5, 36, 26, 18, 12, 8, 6, 6, 49, 37, 27, 19, 13, 9, 7, 7, 64, 50, 38, 28, 20, 14, 10, 8, 8, 81, 65, 51, 39, 29, 21, 15, 11, 9, 9, 100, 82, 66, 52, 40, 30, 22, 16, 12, 10, 10, 121, 101, 83, 67, 53, 41, 31, 23, 17, 13

Offset: 0

Henry Bottomley, Jun 05 2000

			Table begins:
..0...1...4...9..16..25..36..49..64..81.100.121.144...
..1...2...5..10..17..26..37..50..65..82.101.122.145...
..2...3...6..11..18..27..38..51..66..83.102.123.146...
..3...4...7..12..19..28..39..52..67..84.103.124.147...
..4...5...8..13..20..29..40..53..68..85.104.125.148...
..5...6...9..14..21..30..41..54..69..86.105.126.149...
..6...7..10..15..22..31..42..55..70..87.106.127.150...
..7...8..11..16..23..32..43..56..71..88.107.128.151...
..8...9..12..17..24..33..44..57..72..89.108.129.152...
..9..10..13..18..25..34..45..58..73..90.109.130.153...
.10..11..14..19..26..35..46..59..74..91.110.131.154...
... - _Philippe Deléham_, Mar 31 2013

First column is A001477, second column is A000027, first row is A000290, second row is A002522, third row (apart from first term) is A010000, main diagonal is A002378, other diagonals include A028387, A028552, A014209, A002061, A014206, A027688-A027694, each row of A055096 (as upper right triangle) is right hand part of some row of this table

Cf. A185910

A081114 Triangle read by rows: T(n,k) = n*T(n-1,k) + n - k starting at T(n,n)=0.

Original entry on oeis.org

0, 1, 0, 4, 1, 0, 15, 5, 1, 0, 64, 23, 6, 1, 0, 325, 119, 33, 7, 1, 0, 1956, 719, 202, 45, 8, 1, 0, 13699, 5039, 1419, 319, 59, 9, 1, 0, 109600, 40319, 11358, 2557, 476, 75, 10, 1, 0, 986409, 362879, 102229, 23019, 4289, 679, 93, 11, 1, 0, 9864100, 3628799, 1022298, 230197, 42896, 6795, 934, 113, 12, 1, 0

Offset: 0

Henry Bottomley, Apr 16 2003

Taking the triangle into negative values of n and k would produce results close to (k+1)*e*n! - 1, i.e., one less than multiples of A000522 for nonnegative n.

			Triangle begins
    0;
    1,   0;
    4,   1,  0;
   15,   5,  1, 0;
   64,  23,  6, 1, 0;
  325, 119, 33, 7, 1, 0;

Columns include A007526 and A033312.

T(n,k) = if (k==n, 0, n*T(n-1,k) + n - k);
tabl(nn) = {for (n=0, nn, for (k=0, n, print1(T(n, k), ", ");); print(););} \\ Michel Marcus, Jun 16 2019

For k > 0, T(n, k) = ceiling((A001339(k-1)/(k-1)! - (k-1)*e) *n! - 1) where A001339(k-1) = ceiling((k-1)!*(k-1)*e) for k > 1.

T(n, 0) = floor(e*n! - 1) for n > 0; T(n, 1) = n! - 1. T(n, n)=0; T(n, n-1) = n+2; T(n, n-2) = n^2 + 3*n + 5 = A027688(n+1).

More terms from Michel Marcus, Jun 16 2019

A339236 Irregular triangle of incomplete Leonardo numbers read by rows. T(n, k) = 2*(Sum_{j=0..k} binomial(n-j, j)) - 1, for n>=0 and 0<=k<=floor(n/2).

Original entry on oeis.org

1, 1, 1, 3, 1, 5, 1, 7, 9, 1, 9, 15, 1, 11, 23, 25, 1, 13, 33, 41, 1, 15, 45, 65, 67, 1, 17, 59, 99, 109, 1, 19, 75, 145, 175, 177, 1, 21, 93, 205, 275, 287, 1, 23, 113, 281, 421, 463, 465, 1, 25, 135, 375, 627, 739, 753, 1, 27, 159, 489, 909, 1161, 1217, 1219

Offset: 0

Michel Marcus, Nov 28 2020

			Triangle begins:
  1;
  1;
  1, 3;
  1, 5;
  1, 7, 9;
  1, 9, 15;
  1, 11, 23, 25;
  1, 13, 33, 41;
  1, 15, 45, 65, 67;
  1, 17, 59, 99, 109;
  ...

P. Catarino and A. Borges, A Note on Incomplete Leonardo Numbers, INTEGERS 20A (2020) A43.

Cf. A001595 (Leonardo numbers: right diagonal).

Cf. A000012 (column 0), A005408 (column 1), A027688 (column 2).

T[n_, k_] := 2 * Sum[Binomial[n - j, j], {j, 0, k}] - 1; Table[T[n, k], {n, 0, 14}, {k, 0, Floor[n/2]}] // Flatten (* Amiram Eldar, Nov 28 2020 *)

T(n, k) = 2*sum(j=0, k, binomial(n-j, j)) -1;
row(n) = vector(n\2+1, k, k--; T(n,k));

T(n, floor(n/2)) = A001595(n).

cp's OEIS Frontend

A171746 Let f(n) = n + floor(sqrt(n)). Then a(n) is the smallest number of iterations of f on n such that a perfect square is obtained.

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A354902 a(n) = 2*n^2 - 6*n + 11 for n > 1 with a(0)=1 and a(1)=3.

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A214870 Natural numbers placed in table T(n,k) layer by layer. The order of placement: at the beginning filled odd places of layer clockwise, next - even places counterclockwise. T(n,k) read by antidiagonals.

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A268101 Smallest prime p such that some polynomial of the form a*x^2 - b*x + p generates distinct primes in absolute value for x = 1 to n, where 0 < a < p and 0 <= b < p.

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A055630 Table T(k,m) = k^2 + m read by antidiagonals.

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A081114 Triangle read by rows: T(n,k) = n*T(n-1,k) + n - k starting at T(n,n)=0.

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A339236 Irregular triangle of incomplete Leonardo numbers read by rows. T(n, k) = 2*(Sum_{j=0..k} binomial(n-j, j)) - 1, for n>=0 and 0<=k<=floor(n/2).

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A354902 a(n) = 2n^2 - 6n + 11 for n > 1 with a(0)=1 and a(1)=3.

A268101 Smallest prime p such that some polynomial of the form ax^2 - bx + p generates distinct primes in absolute value for x = 1 to n, where 0 < a < p and 0 <= b < p.