The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A052091 Left parts needed for the construction of the palindromic prime pyramid starting with 2. 5
 2, 7, 3, 33, 9, 30, 18, 92, 3, 133, 18, 117, 17, 15, 346, 93, 33, 180, 120, 194, 126, 336, 331, 330, 95, 12, 118, 369, 39, 32, 165, 313, 165, 134, 13, 149, 195, 145, 158, 720, 18, 396, 193, 102, 737, 964, 722, 156, 106, 395, 945, 303, 310, 113, 150, 303, 715, 123 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS Each term is the smallest to have the previous term as a centered substring, beginning with the smallest palindromic prime 2. The right parts are the reversals of the above terms leading zeros included. The terms from a(34) onward currently correspond only to strong pseudoprimes. For n > 0, the leftmost (most significant) digit of a(n) is either 1, 3, 7 or 9. - Chai Wah Wu, Dec 02 2015 LINKS Chai Wah Wu, Table of n, a(n) for n = 0..501 P. De Geest, World!Of Palindromic Primes, Page 3 EXAMPLE Start with 2; add 7 gives 727; add 3 gives 37273; add 33 gives 333727333; etc. PROG (Python) from sympy import isprime A052091_list, p = [2], 2 for _ in range(30):     m, ps = 1, str(p)     s = int('1'+ps+'1')     while not isprime(s):         m += 1         ms = str(m)         if ms[0] in '268':             ms = str(int(ms[0])+1) + '0'*(len(ms)-1)             m = int(ms)         if ms[0] in '45':             ms = '7' + '0'*(len(ms)-1)             m = int(ms)         s = int(ms+ps+ms[::-1])     p = s     A052091_list.append(m) # Chai Wah Wu, Dec 02 2015 CROSSREFS Cf. A053600, A052092, A047076. Sequence in context: A210662 A229610 A117809 * A090276 A249782 A090564 Adjacent sequences:  A052088 A052089 A052090 * A052092 A052093 A052094 KEYWORD nonn,base AUTHOR Patrick De Geest, Jan 15 2000 EXTENSIONS Comments from G. L. Honaker, Jr., Mar 30 2000 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 27 19:34 EDT 2021. Contains 347694 sequences. (Running on oeis4.)