A324921 Index of first occurrence of n in A324920.

0, 1, 2, 3, 10, 11, 26, 83, 178, 179, 362, 1835, 9188, 42709, 162466, 358487, 1877938, 11596979, 57866702, 94418279, 1888365980

Offset

0,3

Links

Table of n, a(n) for n=0..20.

Mathematica

g[n_] := Block[{d = Divisors@ n}, len = Length@ d; If[ OddQ@ len, 0, d[[1 + len/2]] - d[[len/2]]]]; f[n_] := Length@ NestWhileList[g, n, # > 0 &] - 1; t[_] := -1; k = 0; While[k < 1000000001, a = f@ k; If[ t[a] == -1, t[a] = k]; k++]; t@# & /@ Range[0, 17]

Prog

(PARI) a056737(n)=n=divisors(n); n[(2+#n)\2]-n[(1+#n)\2] \\ after M. F. Hasler in A056737
a324920(n) = my(x=n, i=0); while(x!=0, i++; x=a056737(x)); i
a(n) = for(k=0, oo, if(a324920(k)==n, return(k))) \\ Felix Fröhlich, Mar 20 2019

Crossrefs

Cf. A056737, A324920.

Sequence in context: A270474 A008509 A281366 * A307034 A081868 A212103

Adjacent sequences: A324918 A324919 A324920 * A324922 A324923 A324924

Keyword

nonn,more

Author

Robert G. Wilson v, Mar 20 2019

Extensions

a(18)-a(20) from Daniel Suteu, Mar 20 2019

Status

approved