OFFSET
1,1
COMMENTS
tau(n) = A000005(n) is the number of divisors of n.
Observation :
The sequence shows pairs of the form (m, m +/- 1) such as: (6,5), (8,7), (14,13), (34,35), (38,37), (57,58), (62,61), (74,73), (93,94), (94,95), (104,105), (118,119), (135,136), (142,143), (177,178), (188,187), (244,245), ...
EXAMPLE
a(20)=21020 because tau(21020) = 12 = reversal(21) = reversal(21020-20).
MATHEMATICA
Table[k=n+1; While[!(k>n)||!DivisorSigma[0, k]==FromDigits[Reverse[IntegerDigits[k-n]]], k++]; k, {n, 80}]
PROG
(PARI) rev(n) = subst(Polrev(digits(n)), x, 10);
a(n) = {k = n+1; while (numdiv(k) != rev(k-n), k++); k; } \\ Michel Marcus, Apr 23 2014
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Michel Lagneau, Apr 23 2014
STATUS
approved