You may remember that my daughter (Peggy Sue - though most people just call her "Doctor") is a big fan of the number 13. So I have prepared a new NERDY number for her.

The new sequence is called the "Pegganacci Sequence". It starts off like a Tridecanacci Sequence but each new term is the sum of the the prevous 13 terms, each multiplied by one of the numbers from 1 to 13. Mathematicians would explain it this way:

The new NERDY number is:

999999999999899999999999979999999999996 999999999999599999999999949999999999993 999999999999299999999999919999999999990 999999999998999999999999889999999999987

9999999999987.

The the decimal expansion of the inverse of the number shown above is called the "Pegg-anacci Sequence". It starts off like a Tridecanacci Sequence but each new term is the sum of the the previous 13 terms, each multiplied by one of the numbers from 1 to 13. Mathematicians would explain it this way:

This is a Fibonacci like sequence where a(0) = a(1) = a(2) = a(3) = … = a(11) = a(12) = 0, a(13) = 1, and when n>13

then a(n) = a(n – 1) + 2*a(n – 2) + 3*a(n – 3) +

4*a(n – 4) + 5*a(n – 5) + 6*a(n – 6) + 7*a(n – 7) +

8*a(n – 8) + 9*a(n – 9) + 10*a(n – 10) + 11*a(n – 11) + 12*a(n – 12) + 13*a(n – 13). Each term in the sequence is written in 13 digit chunks, which are accurate to the 31

^{st}non-zero term.

The decimal expansion of the inverse is:

__1__

999999999999899999999999979999999999996 999999999999599999999999949999999999993 999999999999299999999999919999999999990 999999999998999999999999889999999999987

9999999999987 =

0.

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000000

0000000000001

0000000000001

0000000000003

0000000000008

0000000000021

0000000000055

0000000000144

0000000000377

0000000000987

0000000002584

0000000006765

0000000017711

0000000046368

0000000121393

0000000317797

0000000831997

0000002178165

0000005702425

0000014928920

0000039083838

0000102321293

0000267876635

0000701299695

0001835999105

0004806636502

0012583750392

0032944195765

0086247740185

0225796153741

0591133204441

1547583781233 …

The new NERDY Number is a 169 digit number (THIRTEEN squared). It produces a sequence where each new term is the sum of the THIRTEEN prior terms, each multiplied by a number from one to THIRTEEN, and written as THIRTEEN digit numbers. It produces 31 accurate non-zero terms (and "31" is "13" written backwards).

Make sure you stick this one away in your notes on "13-ish Trivia".

David

Free-Range Mathematologist

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