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A368855 Index of the first occurrence of n in A076982. 1
1, 2, 3, 8, 14, 15, 39, 20, 44, 35, 195, 119, 104, 594, 224, 384, 455, 539, 440, 560, 3080, 2184, 1539, 2015, 2639, 5264, 4199, 15399, 13299, 8855, 23919, 2079, 30744, 43680, 36575, 14399, 5984, 58695, 113399, 47124, 107184, 12375, 78624, 98175, 73359, 111320, 242879, 185724 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = (sqrt(8*A076983(n)+1)-1)/2. - Amiram Eldar, Jan 10 2024
EXAMPLE
a(1) = 1 since A076982(1) = 1;
a(2) = 2 since A076982(2) = 2;
a(3) = 3 since A076982(3) = 3;
a(4) = 8 since A076982(8) = 4;
a(5) = 14 since A076982(14) = 5; etc.
MATHEMATICA
k = 1; t[_] := 0; f[n_] := Length@ Select[ Divisors[n (n +1)/2], IntegerQ@ Sqrt[8# +1] &]; While[k < 250000, a = f@k; If[ t[a] == 0, t[a] = k]; k++]; t /@ Range@ 48
CROSSREFS
Essentially the same as A225400.
Sequence in context: A153865 A369774 A331820 * A022951 A247124 A171237
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Jan 09 2024
STATUS
approved

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Last modified April 19 19:02 EDT 2024. Contains 371798 sequences. (Running on oeis4.)