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A244551 Numbers n such that n +/- the sum of digits of n are both palindromes. 2
1, 2, 3, 4, 10, 100, 105, 181, 262, 267, 343, 348, 424, 429, 681, 762, 767, 843, 848, 924, 929, 1000, 10000, 100000, 1000000, 10000000, 63999991, 72999982, 81999973, 90999964, 100000000, 1000000000, 10000000000, 100000000000, 1000000000000, 10000000000000, 100000000000000, 1000000000000000, 10000000000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

For k = 0, 1, 2, ..., 10^k is a member of this sequence, so A011557 is a subsequence.

Also, floor(a(n)/10) must be in A244573.

Intersection of A229545 and A229621. - Michel Marcus, Jun 30 2014

The corresponding digit sums are: 1, 2, 3, 4, 1, 1, 6, 10, 10, 15, 10, 15, 10, 15, 15, 15, 20, 15, 20, 15, 20, 1, 1, 1, 1, 1, 55, 55, 55, 55, 1, 1, .... - Derek Orr, Jun 30 2014

When the digits sums are 1, the terms are a power of 10 terms, with corresponding palindromes being 2 apart (consecutive palindromes). The next instances of consecutive palindromes appear when digit sums are 55, so that the palindromes are 110 apart (see sequence A104459 that lists the possible differences between adjacent palindromes). - Michel Marcus, Jul 01 2014

There are infinitely many terms in this sequence that are not of the form 10^k for some k. Take the number 180 {59 9's} 631. This is a 65-digit number (180999...999631). This number is a member of this sequence. From this number, we can generate 34 other numbers. Keeping the 59 9's there, to preserve its properties, subtract 9 from 180 and add 90 to 631. Now we have 171 {59 9's} 721. This is also a member. The 59 9's are only to make the digit sum = 550. Thus, the two palindromes are 1100 apart, they are consecutive. If we keep doing this arithmetic (subtract 9 from the first number and add 90 to the second), we get 162 {59 9's} 811, 153 {59 9's} 901, 144 {58 9's} 991. The last number only has 58 9's in order to make sure the digit sum stays at 550. Other numbers and patterns to them have been listed in an a-file. Similarly, patterns like this will appear when considering digit sums of 5500 and larger. - Derek Orr, Jul 01 2014

LINKS

Table of n, a(n) for n=1..39.

Derek Orr, More terms in the sequence

EXAMPLE

267 - (2+6+7) = 252 is a palindrome and 267 + (2+6+7) = 282 is also a palindrome. Thus 252 is a member of this sequence.

PROG

(PARI) rev(n)={r=""; for(i=1, #digits(n), r=concat(Str(digits(n)[i]), r)); return(eval(r))}

for(n=1, 10^7, dig=digits(n); s=sum(k=1, #dig, dig[k]); sm=n-s; la=n+s; if(rev(sm)==sm&&rev(la)==la, print1(n, ", ")))

(Python)

def palgen(l, b=10): # generator of palindromes in base b of length <= 2*l

    if l > 0:

        yield 0

        for x in range(1, l+1):

            n = b**(x-1)

            n2 = n*b

            for y in range(n, n2):

                k, m = y//b, 0

                while k >= b:

                    k, r = divmod(k, b)

                    m = b*m + r

                yield y*n + b*m + k

            for y in range(n, n2):

                k, m = y, 0

                while k >= b:

                    k, r = divmod(k, b)

                    m = b*m + r

                yield y*n2 + b*m + k

A244551_list = []

for p in palgen(9):

    l = len(str(p))

    for i in range(1, l*9+1):

        n = p-i

        if n > 0:

            if sum((int(d) for d in str(n))) == i:

                s = str(n-i)

                if s == s[::-1]:

                    A244551_list.append(n) # Chai Wah Wu, Aug 24 2015

CROSSREFS

Cf. A229545, A229621, A007953.

Sequence in context: A270375 A049204 A045924 * A068910 A146027 A305619

Adjacent sequences:  A244548 A244549 A244550 * A244552 A244553 A244554

KEYWORD

nonn,base

AUTHOR

Derek Orr, Jun 29 2014

EXTENSIONS

a(27)-a(32) from Michel Marcus, Jun 30 2014

a(33)-a(39) from Chai Wah Wu, Aug 24 2015

STATUS

approved

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Last modified August 9 01:35 EDT 2020. Contains 336310 sequences. (Running on oeis4.)