Thursday 24 December 2015

Double and Reverse Digits

After twelve days, I encountered today the first member of the twin prime pair: 24371 and 24373. It's been a while: the last pair was 24179 and 24181 as far as I can tell. The number is a member of the interesting OEIS A036447 formed using 1 as its starting point and then doubling and reversing the digits:


1, 2, 4, 8, 61, 221, 244, 884, 8671, 24371, ...


The number is also a member of OEIS A243408: primes p such that 10p-1, 10p-3, 10p-7 and 10p-9 are all prime. This means that 243709, 243707, 243703 and 243701 are all prime.

Additionally, the number is a member of OEIS A158641: strong primes p: adding 2 to any one digit of p produces a prime number (no digits 8 & 9 in p). This means that 44371, 26371, 24571, 24391 and 24373 are prime.

There's still more. The number is a member of OEIS A104846: primes from merging of 5 successive digits in decimal expansion of e. Here is part of the sequence (up to 24371):

74713, 62497, 24977, 24709, 47093, 95957, 49669, 27427, 46639, 32003, 59921, 21817, 35729, 63073, 28627, 27943, 94349, 33829, 98807, 57383, 41879, 18793, 91499, 68477, 47741, 37423, 42437, 24371

Lastly, 24371 is also a member of OEIS A054564 as describe below:


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