A074757 Numbers n such that tau(n) = (tau(n+1)+tau(n-1))/2.

34, 46, 62, 74, 86, 94, 142, 188, 202, 214, 218, 231, 243, 244, 262, 278, 302, 356, 375, 394, 422, 423, 428, 436, 446, 459, 478, 494, 584, 596, 604, 621, 628, 634, 664, 698, 716, 837, 861, 885, 903, 916, 922, 944, 956, 982, 1004, 1017, 1018, 1028, 1042, 1052

Offset: 1

Author

Benoit Cloitre, Sep 28 2002

Keywords

• easy
• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• Vaclav Kotesovec, Plot of a(n)/n for n = 1..1000000
• Vaclav Kotesovec, Plot of a(n)/(n*log(log(n))) for n = 1..1000000

Crossrefs

Cf. A090502.

Programs

Mathematica

okQ[{a_,b_,c_}]:=(a+c)/2==b; Flatten[Position[Partition[DivisorSigma[0, Range[1100]],3,1],?okQ]]+1 (* _Harvey P. Dale, Aug 17 2013 *)

Formula

a(n) seems to be asymptotic to c*n with c around 23. [This conjecture is false. The limit a(n)/n, if it exists, is > 29, see graphs. - Vaclav Kotesovec, Feb 14 2019]