A078261 a(n) = numerator(N) where N = 0.246...(2n) is the concatenation of the first n even numbers after the decimal point.

1, 6, 123, 617, 24681, 6170253, 1234050607, 30851265177, 12340506070809, 123405060708091, 123405060708091011, 1542563258851137639, 1234050607080910111213, 61702530354045505560657, 2468101214161820222426283, 308512651770227527803285379, 123405060708091011121314151617

Offset

1,2

Links

Alois P. Heinz, Table of n, a(n) for n = 1..351

Maple

a:= n-> (t-> numer(t/10^length(t)))(parse(cat(2*i$i=1..n))):
seq(a(n), n=1..17);  # Alois P. Heinz, Jun 25 2025

Prog

(PARI) a(n) = {my(s = ""); for (k=1, n, s = concat(s, Str(2*k))); numerator(eval(s)/10^(#s)); } \\ Michel Marcus, Jan 15 2019

Crossrefs

Cf. A078258 (similar, with concatenation of 1 to n), A078260 (denominators).

Sequence in context: A138572 A393626 A356199 * A239752 A193223 A372920

Adjacent sequences: A078258 A078259 A078260 * A078262 A078263 A078264

Keyword

base,nonn

Author

Amarnath Murthy, Nov 24 2002

Extensions

More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 19 2003

More terms from Michel Marcus, Jan 15 2019

Status

approved