A209914 Number of ways n can be written as a multiple of its reversal A004086(n) +/- a prime p < n.

0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 8, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 2, 1, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 1, 0, 0, 0, 0, 2, 3, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 2

Offset: 0

Author

M. F. Hasler, Mar 15 2012

Keywords

• nonn
• base

Comments

If n is not a multiple of 10, then a(n) < 20. The subsequence { a(10k) }, however, is unbounded. In particular, a(10^k)=2*A006880(k).

Examples

			a(10)=8 because R(10)=01=1 and 10 = 3*1 + 7 = 5*1 + 5 = 7*1 + 3 = 8*1 + 2 = 12*1 - 2 = 13*1 - 3 = 15*1 - 5 = 17*1 - 7.
		

Crossrefs

Cf. A209063.

Programs

PARI

a(n)={my(r=A004086(n)); sum(k=1, (2*n-1)\(r+!r), isprime(abs(n-k*r)))}