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A053063 Alternately append n to beginning or end of previous term. 0
1, 21, 213, 4213, 42135, 642135, 6421357, 86421357, 864213579, 10864213579, 1086421357911, 121086421357911, 12108642135791113, 1412108642135791113, 141210864213579111315, 16141210864213579111315, 1614121086421357911131517, 181614121086421357911131517, 18161412108642135791113151719 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

Felice Russo, A set of new Smarandache functions, sequences and conjectures in number theory, American Research Press 2000

LINKS

Table of n, a(n) for n=1..19.

FORMULA

a(n) = (1/2)*(1 + (-1)^n)*(n*10^(floor(1 + log_10(a(n-1)))) + a(n-1)) + (1/2)*(1 - (-1)^n)*(a(n-1)*10^(floor(1 + log_10(n))) + n), with a(0)=1. - Paolo P. Lava, Oct 29 2008

MAPLE

P:=proc(i) local a, n; a:=1; print(a); for n from 2 by 1 to i do a:=1/2*(1+(-1)^n)*(n*10^trunc(evalf(floor(1+log10(a)), 100))+a)+1/2*(1-(-1)^n)*(a*10^trunc(evalf(floor(1+log10(n)), 100))+n); print(a); od; end: P(100); # Paolo P. Lava, Oct 29 2008

PROG

(PARI) lista(nn) = {print1(val=1, ", "); b = 0; for (n=2, nn, if (b, val = concat(Str(val), Str(n)), val = concat(Str(n), Str(val))); print1(val, ", "); b = 1 - b; ); } \\ Michel Marcus, Aug 11 2017

CROSSREFS

Sequence in context: A133355 A041846 A120786 * A060933 A075282 A228681

Adjacent sequences:  A053060 A053061 A053062 * A053064 A053065 A053066

KEYWORD

easy,nonn,base,less

AUTHOR

Felice Russo, Feb 25 2000

EXTENSIONS

More terms from Michel Marcus, Aug 11 2017

STATUS

approved

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Last modified March 26 01:08 EDT 2019. Contains 321479 sequences. (Running on oeis4.)