Demonstration of the

On-Line Encyclopedia of Integer Sequences® (OEIS®)

(Page 4)

Identifying a Sequence: a Puzzle

Many users of the OEIS are attempting to solve puzzles. This has always been one of its main applications, and the database includes a large number of the standard puzzle sequences.

In this next example you could be anyone in the world who uses Arabic numerals - a primary school student in England studying for an I.Q. test or a businessman in India reading the puzzle column of a newspaper.

You are asked to explain this sequence and find the next term:

61, 52, 63, 94, 46, ....

You decide to ask the OEIS for help.

As in the previous two demonstrations, you go to the main web page and enter the sequence.

This produces the following response.

Greetings from the On-Line Encyclopedia of Integer Sequences!

A002942 Squares written backwards. (Formerly M3370 N1357) +0 5

1, 4, 9, 61, 52, 63, 94, 46, 18, 1, 121, 441, 961, 691, 522, 652, 982, 423, 163, 4, 144, 484, 925, 675, 526, 676, 927, 487, 148, 9, 169, 4201, 9801, 6511, 5221, 6921, 9631, 4441, 1251, 61, 1861, 4671, 9481, 6391, 5202, 6112, 9022, 4032, 1042, 52, 1062 (list)

OFFSET 1,2 EXAMPLE For example, 12*12 = 144, which written backwards is 441, so a(12) = 441. 10*10 = 100, so a(10) = 001 = 1. CROSSREFS Cf. A000290, A080334. Sequence in context: A086692 A069507 A013571 this_sequence A028908 A073658 A059479 Adjacent sequences: A002939 A002940 A002941 this_sequence A002943 A002944 A002945 KEYWORD nonn,base,easy AUTHOR njas EXTENSIONS More terms from Jeremy Gardiner (jeremy.gardiner(AT)btinternet.com), Sep 08 2002

page 1

Ah yes, 61 is 16 = 4 x 4 written backwards!
You resolve to remember this answer next time you see the problem (or failing that, the existence of this web site)!

Other sequences from tests and quizzes can be found in the Puzzle sequences web page (but then you will have to use the Back button on your browser to return to these demonstrations). Of course many others can be found by using the webcam to browse the OEIS.

Click the single right arrow to go to the next demonstration page, or the single left arrow to return to the previous page.