A083140 Sieve of Eratosthenes arranged as an array and read by antidiagonals in the up direction; n-th row has property that smallest prime factor is prime(n).

2, 3, 4, 5, 9, 6, 7, 25, 15, 8, 11, 49, 35, 21, 10, 13, 121, 77, 55, 27, 12, 17, 169, 143, 91, 65, 33, 14, 19, 289, 221, 187, 119, 85, 39, 16, 23, 361, 323, 247, 209, 133, 95, 45, 18, 29, 529, 437, 391, 299, 253, 161, 115, 51, 20, 31, 841, 667, 551, 493, 377, 319, 203, 125, 57, 22

Offset

2,1

Comments

A permutation of natural numbers >= 2.

The proportion of integers in the n-th row of the array is given by A005867(n-1)/A002110(n) = A038110(n)/A038111(n). - Peter Kagey, Jun 03 2019, based on comments by Jamie Morken and discussion with Tom Hanlon.

The proportion of the integers after the n-th row of the array is given by A005867(n)/A002110(n). - Tom Hanlon, Jun 08 2019

Links

Ivan Neretin, Table of n, a(n) for n = 2..5051

Index entries for sequences that are permutations of the natural numbers

Index entries for sequences generated by sieves

Example

Array begins:
   2   4   6   8  10  12  14  16  18  20  22  24 .... (A005843 \ {0})
   3   9  15  21  27  33  39  45  51  57  63  69 .... (A016945)
   5  25  35  55  65  85  95 115 125 145 155 175 .... (A084967)
   7  49  77  91 119 133 161 203 217 259 287 301 .... (A084968)
  11 121 143 187 209 253 319 341 407 451 473 517 .... (A084969)
  13 169 221 247 299 377 403 481 533 559 611 689 .... (A084970)

Mathematica

a = Join[ {Table[2n, {n, 1, 12}]}, Table[ Take[ Prime[n]*Select[ Range[100], GCD[ Prime[n] #, Product[ Prime[i], {i, 1, n - 1}]] == 1 &], 12], {n, 2, 12}]]; Flatten[ Table[ a[[i, n - i]], {n, 2, 12}, {i, n - 1, 1, -1}]]
(* second program: *)
rows = 12; Clear[T]; Do[For[m = p = Prime[n]; k = 1, k <= rows, m += p, If[ FactorInteger[m][[1, 1]] == p, T[n, k++] = m]], {n, rows}]; Table[T[n - k + 1, k], {n, rows}, {k, n}] // Flatten (* Jean-François Alcover, Mar 08 2016 *)

Crossrefs

Cf. A083141 (main diagonal), A083221 (transpose), A004280, A038179, A084967, A084968, A084969, A084970, A084971.

Arrays of integers grouped into rows by various criteria:

by greatest prime factor: A125624,

by lowest prime factor: this sequence (upward antidiagonals), A083221 (downward antidiagonals),

by number of distinct prime factors: A125666,

by number of prime factors counted with multiplicity: A078840,

by prime signature: A095904,

by ordered prime signature: A096153,

by number of divisors: A119586,

by number of 1's in binary expansion: A066884 (upward), A067576 (downward),

by distance to next prime: A192179.

Cf. A002110, A005867, A038110, A038111.

Sequence in context: A119586 A095904 A096153 * A246279 A285112 A253565

Adjacent sequences: A083137 A083138 A083139 * A083141 A083142 A083143

Keyword

nonn,tabl,nice

Author

Yasutoshi Kohmoto, Jun 05 2003

Extensions

More terms from Hugo Pfoertner and Robert G. Wilson v, Jun 13 2003

Status

approved