A195758 Lesser prime factor of n-th Blum number.

3, 3, 3, 3, 7, 3, 3, 7, 3, 7, 3, 3, 11, 3, 7, 3, 3, 11, 7, 3, 3, 7, 11, 3, 3, 7, 3, 19, 3, 7, 11, 3, 7, 3, 11, 3, 7, 3, 7, 19, 3, 3, 11, 3, 3, 23, 3, 7, 11, 7, 3, 11, 3, 3, 19, 3, 11, 7, 19, 11, 7, 3, 3, 7, 23, 3, 3, 7, 3, 23, 3, 19, 11, 3, 7, 3, 7, 11, 7, 3

Offset: 1

Author

Reinhard Zumkeller, Sep 23 2011

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
• Wikipedia, Blum integer

Crossrefs

Cf. A096916.

Programs

Haskell

a195758 = a020639 . a016105

Mathematica

Take[Transpose[SortBy[{#[[1]],#[[2]],#[[1]]#[[2]]}&/@With[{c=Select[ 4*Range[ 0,200]+3,PrimeQ]},Subsets[c,{2}]],Last]][[1]],90] (* Harvey P. Dale, May 20 2012 *)

Formula

a(n) * A195759(n) = A016105(n); a(n) < A195759(n);

a(n) = A020639(A016105(n)).