A118667 a(n) = a(n-1)+ (abs(2^a(n-1)*a(n-1)) mod 10).

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

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

Harvey P. Dale, Table of n, a(n) for n = 0..250

Formula

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

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);

Mathematica

Join[{0}, NestList[#+Mod[Abs[2^# #], 10]&, 1, 60]] (* Harvey P. Dale, Jul 01 2022 *)

Crossrefs

Sequence in context: A310257 A310258 A310259 * A353357 A352140 A258117

Adjacent sequences: A118664 A118665 A118666 * A118668 A118669 A118670

Keyword

nonn

Author

Paolo P. Lava and Giorgio Balzarotti, May 19 2006

Status

approved