cp's OEIS Frontend

William Maness, Oct 24 2011, observes that so far the terms are all odd numbers and the numbers of digits is alternately 2 and 3. Sequence is likely from a book of math puzzles for grade school.

Possible solution is a(1) = 5; a(n) = 5 + 5 * n * A215148(n-1), giving 5, 15, 365, 945, 1755, 2795, 4065, 5565, 7295, 9255, 11445, 13865, 16515, 19395, ... . - Michal Paulovic, Sep 15 2023

Comment from Joshua Zucker, May 26 2007. This appears to be a concatenation of five puzzles:

98,72,77,49,54,20,25,10,15,5,10,0,5,5,10,0,5,5,10,0,... (start with 98, then write down the product of its digits, then add 5, repeat) - see A129887.

10,1,11,2,13,4,17,8,25,7,... (start with 10; write down the sum of its digits; add last two terms; repeat) - see A129888.

1,2,2,6,3,12,4,20,5,30,6,42,... (write down n, then n(n+1)) - see A129889.

15,20,13,18,11,16,9,14,... (interleave two arithmetic progressions of difference -2).

0,0,4,9,8,18,12,27,16,36,20,... (interleave two arithmetic progressions 0,4,8,12,... and 0,9,18,27,...)

If anyone can supply more information about this sequence, please let me know. - N. J. A. Sloane

Possibly an erroneous version of A112667? - R. J. Mathar, Apr 04 2007