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A034111
Fractional part of square root of a(n) starts with 5: first term of runs.
1
21, 31, 43, 57, 73, 91, 111, 133, 157, 183, 211, 241, 273, 307, 343, 381, 421, 463, 507, 553, 601, 651, 703, 757, 813, 871, 931, 993, 1057, 1123, 1191, 1261, 1333, 1407, 1483, 1561, 1641, 1723, 1807, 1893, 1981, 2071, 2163, 2257, 2353, 2451, 2551, 2653
OFFSET
1,1
COMMENTS
Agrees with sequence A002061 (n^2-n+1 = central polygonal numbers) starting with sixth term.
FORMULA
a(n) = n^2 + 7*n + 13. - Charles R Greathouse IV, Aug 10 2010
MATHEMATICA
Array[#^2 + 7 # + 13 &, 48] (* Michael De Vlieger, Aug 05 2020 *)
LinearRecurrence[{3, -3, 1}, {21, 31, 43}, 50] (* Harvey P. Dale, Apr 29 2022 *)
PROG
(PARI) a(n)=n^2+7*n+13 \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
Cf. A034101.
Sequence in context: A168000 A031889 A034101 * A077687 A113762 A032585
KEYWORD
nonn,base,easy
AUTHOR
Patrick De Geest, Sep 15 1998
EXTENSIONS
Offset 1 from Alois P. Heinz, Aug 05 2020
STATUS
approved