A113458 -id:A113458 - cp's OEIS frontend

A113456 Square array read by antidiagonals: a(n, d) is the smallest number that begins an arithmetic progression with common difference d of n numbers with the same prime signature.

1, 2, 1, 33, 3, 1, 19940, 3, 2, 1, 204323, 213, 155, 3, 1, 380480345, 213, 7572, 3, 2, 1

Offset: 1

David Wasserman, Jan 08 2006; corrected Jan 08 2006

First two columns are A034173 and A113457. First three rows are A000012, A086489 and A113458.

			a(3, 2) = 3 because 3, 5 and 7 have the same prime signature.

A113467 Least k such that k, k+n and k+2n have the same number of divisors.

Original entry on oeis.org

33, 3, 119, 3, 77, 5, 8, 3, 77, 3, 35, 5, 8, 3, 187, 6, 21, 5, 8, 3, 145, 33, 39, 5, 8, 39, 8, 3, 33, 7, 15, 12, 189, 3, 28, 7, 21, 3, 55, 3, 33, 5, 8, 66, 209, 69, 35, 5, 8, 3, 115, 39, 141, 5, 51, 6, 8, 27, 15, 7, 21, 66, 95, 3, 40, 5, 27, 3, 8, 15, 35, 7, 69, 55, 287, 6, 65, 11, 8, 3, 24

Offset: 1

David Wasserman, Jan 08 2006

Third row of A113465.

			a(7) = 8 because 8, 15 and 22 each have 4 divisors.

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Cf. A005238, A113458, A113465.

snd[n_]:=Module[{k=1},While[Length[Union[DivisorSigma[0,{k,k+n,k+2n}]]]>1, k++];k]; Array[snd,90] (* Harvey P. Dale, Aug 20 2017 *)

a(n) = {k  = 1; until ((numdiv(k) == numdiv(k+n)) && (numdiv(k) == numdiv(k+2*n)), k++); return (k);} \\ Michel Marcus, Jun 16 2013

cp's OEIS Frontend

A113456 Square array read by antidiagonals: a(n, d) is the smallest number that begins an arithmetic progression with common difference d of n numbers with the same prime signature.

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A113467 Least k such that k, k+n and k+2n have the same number of divisors.

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