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A305673 Indices i where a run of zeros starts in A305671. 5
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 29 00:02 EST 2023. Contains 359905 sequences. (Running on oeis4.)