A091781 Beginning with 1, sum of all possible strings obtained as concatenation of previous (successive) terms.

1, 1, 13, 1252, 12396260, 1239500874377560, 12395008619813008676506120642920, 1239500861981300743700524626536099160068958504069412048965143360, 12395008619813007437005246265360867650603386910607355428445004411155507757831706693304721638824892440620626536624708440686290240

Offset

0,3

Comments

a(n) is the sum of n(n+1)/2 such strings. a(n) has roughly 2^(n-1) decimal digits. - R. J. Mathar, Jul 26 2007

Links

Table of n, a(n) for n=0..8.

Example

a(0) = 1 hence a(1) = 1, a(2) = (1)+(1)+ (11) = 13, a(3) = (1) +(1) +(13) + (11) + (113) + (1113) = 1252.

Maple

A055642 := proc(n) if n <= 1 then 1 ; else ilog10(n)+ 1; fi ; end: Lcat := proc(L, i, j) local resul, k ; resul := 0 ; for k in op(i..j, L) do resul := resul*10^A055642(k)+k ; od ; RETURN(resul) ; end: A091781 := proc(nmax) local a, anxt, n, i, j; a := [1] ; for n from 1 to nmax do anxt := 0 ; for i from 1 to nops(a) do for j from i to nops(a) do anxt := anxt+Lcat(a, i, j) : od ; od ; a := [op(a), anxt] ; od; RETURN(a) ; end: A091781(9) ; # R. J. Mathar, Jul 26 2007

Crossrefs

Cf. A091782.

Sequence in context: A226095 A220619 A178560 * A156641 A300592 A221690

Adjacent sequences: A091778 A091779 A091780 * A091782 A091783 A091784

Keyword

base,nonn

Author

Amarnath Murthy, Feb 17 2004

Extensions

a(4) and a(5) from Donald Sampson (marsquo(AT)hotmail.com), Sep 17 2004

More terms from R. J. Mathar, Jul 26 2007

Status

approved