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A051070
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a(n) is the n-th term in sequence A_n, respecting the offset, or a(n) = -1 if A_n has fewer than n terms.
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7
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1, 2, 1, 0, 2, 3, 0, 7, 8, 4, 63, 1, 316, 78, 16, 2048, 7652, 26627, 8, 24000, 232919, 1145406, 3498690007594650042368, 2058537, 58, 26, 27, 59, 9272780, 3, 69273668, 4870847, 2387010102192469724605148123694256128, 1, 1, -53, 43, 0, -4696, 173, 44583, 111111111111111111111111111111111111111111, 30402457, 668803781, 1134903170, 382443020332
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OFFSET
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1,2
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COMMENTS
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a(58) = A000058(58) = 192523...920807 (58669977298272603 digits) is too large to include in the b-file. - Pontus von Brömssen, May 19 2022
Note that a(n) = -1 can arise in two ways: either A_n has fewer than n terms, or A_n has at least n terms, but its n-th term is -1.
Here is a summary of the terms with n <= 80.
a(n) = -1 occurs just twice, for n = 53 and 54, in both cases because the relevant New York subway lines do not have enough stops.
a(1) though a(65) are known, although a(58) = = 192523...920807 has 58669977298272603 digits.
a(66) is the first unknown value.
Also unknown for n <= 80 are a(67), a(72), a(74), a(75), a(76), and a(77) (counts of numbers <= 2^n represented by various quadratic forms; some of these do not even have b-files), and a(80), which like a(66) is a graph-theory question. (End)
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LINKS
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EXAMPLE
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a(20) = 24000 because A000020(20) = 24000.
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MAPLE
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for m from 1 do
url:= sprintf("https://oeis.org/A%06d/b%06d.txt", m, m);
S:= URL:-Get(url);
L:= StringTools[Split](S, "\n");
for t in L do
g:= sscanf(t, "%d %d");
if nops(g) = 2 and g[1] = m then
a[m]:= g[2];
break
fi;
od;
if not assigned(a[m]) then break fi;
od:
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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EXTENSIONS
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a(36) and a(42) corrected and a(43) to a(46) added by Robert Israel, May 31 2015
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STATUS
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approved
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