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A118667 a(n) = a(n-1)+ ((abs(2^a(n-1)*a(n-1)) mod 10). 0
0, 1, 3, 7, 13, 19, 21, 23, 27, 33, 39, 41, 43, 47, 53, 59, 61, 63, 67, 73, 79, 81, 83, 87, 93, 99, 101, 103, 107, 113, 119, 121, 123, 127, 133, 139, 141, 143, 147, 153, 159, 161, 163, 167, 173, 179, 181, 183, 187, 193, 199, 201, 203, 207, 213, 219, 221, 223, 227, 233 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Apart from the first two terms all the other numbers can be formed adding in sequence 2, 4, 6, 6, 2 and so on. Example 1+(2)=3; 3+(4)=7; 7+(6)=13; 13+(6)=19; 19+(2)=21; ...

LINKS

Table of n, a(n) for n=0..59.

FORMULA

a(n) = a(n-1)+ ((abs(2^a(n-1)*a(n-1)) mod 10) being a(0) = 0 and a(1) = 1

a(n)=(2/5)*Sum{k=0..n-1}{3*(k mod 5)+[(k+1) mod 5]+[(k+4) mod 5]}-1+[C(2*n,n) mod 2], with n>=0 [From Paolo P. Lava, Oct 07 2008]

EXAMPLE

a(2)= 1 + abs(2^1 *1)mod 10 = 1 + 2 mod 10 = 1 + 2 = 3

MAPLE

ANM:=proc(N) local an, i, anminus1, anplus1; anminus1:=0; an:=1; print (anminus1); print (an); for i from 2 by 1 to N do anplus1:=an+(abs(2^an*an) mod 10); print(anplus1); anminus1:=an; an:=anplus1; od; end: ANM(100);

CROSSREFS

Sequence in context: A310257 A310258 A310259 * A258117 A034017 A034021

Adjacent sequences:  A118664 A118665 A118666 * A118668 A118669 A118670

KEYWORD

nonn

AUTHOR

Paolo P. Lava and Giorgio Balzarotti, May 19 2006

STATUS

approved

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Last modified December 4 04:22 EST 2020. Contains 338921 sequences. (Running on oeis4.)