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A028553 Numbers n such that n(n+3) is a palindrome. 3
0, 1, 8, 28, 66, 88, 211, 298, 671, 2126, 2998, 28814, 29369, 29998, 63701, 212206, 212671, 299998, 636776, 2122206, 2861419, 2999998, 9443423, 21341691, 28862883, 29999998, 212325206, 289053683, 294127328, 294174669, 299999998, 2134473706, 2946920844, 2999999998 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Also: sum of the first n even composites is palindromic. Sequence is 4 + 6 + 8 + 10 + 12 + 14 + ... + z. For values of z see A058851. (Comment added by author 12/2000).

3*10^n-2 for n >= 0 are terms. For n>1, a(n) mod 10 is one of {1,3,4,6,8,9}. - Chai Wah Wu, Feb 20 2021

LINKS

Chai Wah Wu, Table of n, a(n) for n = 1..40

P. De Geest, Palindromic Quasipronics

P. De Geest, Palindromic Sums 2

Erich Friedman, What's Special About This Number? (See entries 298, 2126, 2998.)

PROG

(Python)

n, m, A028553_list = 0, 0, []

while n < 10**12:

    s = str(m)

    if s == s[::-1]:

        A028553_list.append(n)

    m += 2*(n+2)

    n += 1 # Chai Wah Wu, Feb 20 2021

CROSSREFS

Cf. A058852, A028554.

Sequence in context: A007259 A134747 A083013 * A100182 A321237 A328535

Adjacent sequences:  A028550 A028551 A028552 * A028554 A028555 A028556

KEYWORD

nonn,base,changed

AUTHOR

Patrick De Geest

EXTENSIONS

More terms from Chai Wah Wu, Feb 20 2021

STATUS

approved

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Last modified March 5 02:54 EST 2021. Contains 341814 sequences. (Running on oeis4.)