A305673 - OEIS

A305673

Indices i where a run of zeros starts in A305671.

2, 15, 55, 108, 195, 256, 370, 419, 437, 782, 1616, 1857, 3055, 4806, 5851, 6142, 6275, 6487, 7161, 7278, 7591, 13041, 13122, 13179, 14904, 14979, 15451, 21767, 32056, 39478, 79649, 148518, 174716, 273952, 400581

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OFFSET

1,1

COMMENTS

Numbers i such that A305671(i) = 0 and A305671(i-1) != 0.

LINKS

Table of n, a(n) for n=1..35.

MATHEMATICA

Block[{c = Select[Range[10^3], CompositeQ], s}, s = DivisorSigma[1, c]; Select[SplitBy[Partition[Position[Array[If[Length@ # == 1, #[[1, 1]], 0] &@ Last@ SplitBy[SortBy[Tally@ Take[s, #], Last], Last] &, Length@ s], 0][[All, 1]], 2, 1], Differences], Length@ # > 1 &][[All, 1, 1]]] (* Michael De Vlieger, Jun 14 2018 *)

PROG

(PARI) mcv(v) = my(w=vecsort(v, , 8), count=vector(#w), ind=0, i=0); for(x=1, #w, for(y=1, #v, if(w[x]==v[y], count[x]++))); for(k=1, #count, if(count[k]==vecmax(count), ind=k; i++)); if(i > 1, return(0), return(w[ind]))

my(v=[], i=1, t=0); forcomposite(c=1, , v=concat(v, [sigma(c)]); if(mcv(v)==0, if(t==0, print1(i, ", ")); t++, t=0); i++)

CROSSREFS

Cf. A305671, A305672, A305674, A305675, A305676.

Sequence in context: A216333 A056078 A142861 * A268761 A088979 A265909

Adjacent sequences: A305670 A305671 A305672 * A305674 A305675 A305676

KEYWORD

nonn,more

AUTHOR

Felix Fröhlich, Jun 08 2018

EXTENSIONS

More terms from Michael De Vlieger, Jun 14 2018

STATUS

approved