# [seqfan] Re: Palindromic Subsequences Of Prime Differences

franktaw at netscape.net franktaw at netscape.net
Fri Mar 26 03:51:16 CET 2010

```You're right, of course; I was just using Leroy's values, even though I
knew they were hand calculated.

A055380 has the mid-points of the even-numbered sequences:

5, 18731, 683783, 98303927, 60335249959, 1169769749219

which gives us for the primes:

3, 18713, 683747, 98303867, 60335249851, 1169769749111

and so on to:

2, 3, 5, 18713, 5, 683747, 17, 98303867, 13, 60335249851, 137,
1169769749111

(a(11) = 137 is by observation of A001223; I'm pretty sure it's right.)

I can't determine indices of those larger primes with PARI; maybe
somebody else can.

Franklin T. Adams-Watters

-----Original Message-----
From: Hans Havermann <pxp at rogers.com>

> The sequence of prime indices, 1,2,3,2136,4,...

I think it's 1, 2, 3, 2136, 3*, 55337, 7, 5669438, 6, ...

for primes 2, 3, 5, 18713, 5* (not 7), 683747, 17, 98303867, 13, ...

For the even terms, cf. A006562 (Balanced primes of order one:
5, ...), A051795 (Doubly balanced primes: 18731, ...), A081415 (Triply
balanced primes: 683783, ...), A096710 (Quadruply balanced primes:
98303927, ...).

```

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