A028990 Largest palindromic prime with 2n-1 digits.

7, 929, 98689, 9989899, 999727999, 99999199999, 9999987899999, 999999787999999, 99999999299999999, 9999999992999999999, 999999999757999999999, 99999999997579999999999

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Comments

For n>1, since 11 is a proper divisor of a palindrome with 2n digits, the numbers a(n) and A028989(n+1) are consecutive in A002385. - Jeppe Stig Nielsen, Feb 20 2021

Links

• Jeppe Stig Nielsen, Table of n, a(n) for n = 1..500
• Patrick De Geest, World!Of Palindromic Primes

Crossrefs

Cf. A002385, A028989.

Programs

PARI

a(n)=forstep(j=10^n-1,10^(n-1),-1,my(d=digits(j), p=fromdigits(vector(2*n-1,x,if(xJeppe Stig Nielsen, Feb 20 2021

Extensions

Offset changed (as it was in A028989) by Jeppe Stig Nielsen, Feb 20 2021