OFFSET

1,3

EXAMPLE

7337 is in the sequence because (1) it is an icosagonal number and (2) the sum of the digits 7+3+3+7=20 is also an icosagonal number.

PROG

(PARI) isok(n) = ispolygonal(n, 20) && ispolygonal(sumdigits(n), 20); \\ Michel Marcus, Feb 27 2014

CROSSREFS

KEYWORD

nonn,base

AUTHOR

Luc Stevens (lms022(AT)yahoo.com), Apr 29 2006

EXTENSIONS

a(11) corrected by Georg Fischer, Mar 27 2024

STATUS

approved