

A137779


Number of bases (numbering systems, including unary) in which the nth prime is a palindrome having at least two digits.


2



1, 2, 3, 3, 2, 3, 4, 2, 3, 3, 4, 3, 3, 3, 2, 2, 3, 3, 4, 3, 4, 2, 3, 3, 3, 3, 2, 4, 4, 3, 4, 3, 2, 2, 2, 4, 4, 2, 2, 4, 2, 4, 5, 3, 4, 3, 4, 2, 4, 3, 3, 3, 4, 3, 6, 2, 2, 4, 4, 3, 2, 2, 4, 2, 5, 2, 3, 5, 2, 3, 5, 2, 2, 6, 5, 3, 2, 3, 4, 4, 4, 5, 3, 4, 2, 5, 3, 4, 4, 4, 3, 3, 4, 2, 3, 3, 3, 4, 4
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OFFSET

1,2


COMMENTS

Each prime p > 2 is palindrome in at least base 1 and base p1, since p = 1*(p1)^1 + 1*(p1)^0 and p = 1*1^(p1) + 1*1(p2) + ... + 1*1^1 + 1*1^0.


LINKS

Attila Olah, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = A126071(prime(n)).  Charles R Greathouse IV, Jun 19 2014


EXAMPLE

a(621) = 9 because the 621st prime (4591) is a palindrome in 9 bases: base 1, 19, 20, 24, 33, 37, 51, 54 and 4590 (4591 = 1*4590^1 + 1*4590^0).


PROG

(PARI) ispal(v) = {for(i=1, #v\2, if (v[i] != v[#vi+1], return(0)); ); return(1); };
a(n) = {p = prime(n); 1 + sum(i=2, p, ispal(digits(p, i))); } \\ Michel Marcus, Sep 04 2013


CROSSREFS

Cf. A087911, A126071.
Sequence in context: A296611 A308661 A286104 * A191246 A248222 A107918
Adjacent sequences: A137776 A137777 A137778 * A137780 A137781 A137782


KEYWORD

easy,base,nonn


AUTHOR

Attila Olah (jolafix(AT)gmail.com), May 06 2008, corrected May 08 2008


STATUS

approved



