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A076612 Palindromic numbers with nonprime middle digit. 0
1, 4, 6, 8, 9, 101, 111, 141, 161, 181, 191, 202, 212, 242, 262, 282, 292, 303, 313, 343, 363, 383, 393, 404, 414, 444, 464, 484, 494, 505, 515, 545, 565, 585, 595, 606, 616, 646, 666, 686, 696, 707, 717, 747, 767, 787, 797, 808, 818, 848, 868, 888, 898, 909 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

a(12)=202=2*101 is palindromic number and its middle digit 0 is not prime, a(13)=212=2^2*53 is palindromic number and its middle digit 1 is not prime, a(14)=242=2*11^2 is palindromic number and its middle digit 4 is not prime, ...

MAPLE

ts_num_midpal := proc(n) local ad, adr, midigit; ad := convert(n, base, 10): adr := ListTools[Reverse](ad): if nops(ad) mod 2 = 0 then return 1; fi; midigit := op( (nops(ad)+1)/2, ad ): if (isprime( midigit )='false' and adr=ad) then return 0; else return 1; fi end: ts_n_pal := proc(n) if ts_num_midpal(n) = 0 then return (i) fi end: anpal := [seq(ts_n_pal(i), i=1..50000)]: anpal;

CROSSREFS

Cf. A002113.

Sequence in context: A202262 A202266 A232541 * A182775 A046354 A046357

Adjacent sequences:  A076609 A076610 A076611 * A076613 A076614 A076615

KEYWORD

easy,nonn,base

AUTHOR

Jani Melik, Oct 21 2002

STATUS

approved

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Last modified October 23 11:48 EDT 2019. Contains 328345 sequences. (Running on oeis4.)