A324920 -id:A324920 - cp's OEIS frontend

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

Robert G. Wilson v, Mar 20 2019

Cf. A056737, A324920.

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]

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

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

A307034 a(n) is the smallest integer k of the form k = x*(x + a(n-1)), such that A324920(k) = n, for some positive integer x, with a(0) = 0.

Original entry on oeis.org

0, 1, 2, 3, 10, 11, 26, 87, 178, 179, 362, 1835, 22164, 155197, 620804, 5587317, 55873270, 167619819, 1340958616, 57661222337, 345967334058, 25255615391563, 858690923314298, 4293454616571515, 60108364632001406, 3185743325496077327, 178401626227780333448, 1605614636050023001113

Offset: 0

Daniel Suteu and Robert G. Wilson v, Mar 23 2019

nonn

Inspired by A324921.

This sequence provides upper bounds for A324921, i.e.: A324921(n) <= a(n).

Cf. A056737, A324920, A324921.

f(n) = my(d=divisors(n)); d[(2+#d)\2]-d[(1+#d)\2]; \\ A056737
g(n) = my(k=0); while(n!=0, k++; n=f(n)); k; \\ A324920
a(n) = if(n <= 0, return(0)); my(t=a(n-1)); for(k=1, oo, if(g(k*(k+t)) == n, return(k*(k+t))));

cp's OEIS Frontend

A324921 Index of first occurrence of n in A324920.

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