A305672 Indices i where a run of nonzero values starts in A305671.

1, 8, 35, 88, 162, 225, 363, 386, 427, 508, 998, 1633, 1901, 3091, 4816, 5905, 6179, 6297, 6674, 7221, 7293, 7715, 13100, 13130, 13238, 14927, 15012, 15520, 22413, 32219, 39561, 79864, 148622, 175500, 274750, 402174

Offset

1,2

Comments

For n > 1, numbers i such that A305671(i) != 0 and A305671(i-1) = 0.

Links

Table of n, a(n) for n=1..36.

Mathematica

Block[{c = Select[Range[10^4], CompositeQ], s}, s = DivisorSigma[1, c]; Prepend[1 + Accumulate[Total /@ #], #[[1, 1]]] &@ Partition[Length /@ SplitBy[#, # == 0 &], 2, 2] &@ Array[If[Length@ # == 1, #[[1, 1]], 0] &@ Last@ SplitBy[SortBy[Tally@ Take[s, #], Last], Last] &, Length@ s]] (* Michael De Vlieger, Jul 21 2018 *)

Prog

(PARI) my(v=[], i=0, b=0, idx=1); forcomposite(c=1, , my(sig=sigma(c)); if(#v < sig, v=concat(v, vector(sig-#v))); v[sig]++; for(k=1, #v, if(v[k]==vecmax(v), i++)); if(i < 2, if(b==0, print1(idx, ", "); b=1)); if(i > 1, b=0); idx++; i=0)

Crossrefs

Cf. A305671, A305673, A305674, A305675, A305676.

Sequence in context: A214725 A136016 A257454 * A100907 A303383 A265840

Adjacent sequences: A305669 A305670 A305671 * A305673 A305674 A305675

Keyword

nonn,more

Author

Felix Fröhlich, Jun 08 2018

Status

approved