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A344871
a(n) is the least number that can be represented in exactly n ways as the sum of a prime and its digit reversal.
1
1, 4, 44, 88, 1090, 3212, 4334, 2992, 5995, 4994, 7997, 9779, 5104, 11110, 11891, 10109, 11000, 10780, 108880, 110500, 252142, 278872, 296692, 293282, 308902, 287782, 411103, 289982, 466664, 281072, 457754, 398893, 298892, 462154, 517814, 494384, 299992, 707806, 471064, 476674, 487784, 467764
OFFSET
0,2
COMMENTS
If the reversal of p is another prime, p+reversal(p) and reversal(p)+p are both counted.
a(n) is the first number that occurs exactly n times in A061227.
LINKS
EXAMPLE
a(4) = 1090 because 1090 = 149+941 = 347+743 = 743+347 = 941+149, and this is the least number with exactly four such representations.
MAPLE
revdigs:= proc(n) local L, t;
L:= convert(n, base, 10);
add(L[-t]*10^(t-1), t=1..nops(L));
end proc:
V:= Vector(10^6):
p:= 1:
do
p:= nextprime(p);
if p > 9*10^5 then break fi;
r:= p+revdigs(p);
if r <= 10^6 then V[r]:= V[r]+1 fi
od:
A:= Array(0..64):
for i from 1 to 10^6 do
if V[i] <= 64 and A[V[i]] = 0 then A[V[i]]:= i fi
od:
convert(A, list);
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, May 31 2021
STATUS
approved