A320881 Numbers equal to a prime plus its digit sum.
4, 6, 10, 13, 14, 17, 25, 28, 29, 35, 40, 46, 47, 50, 58, 61, 68, 73, 79, 80, 83, 94, 95, 103, 106, 107, 113, 115, 118, 119, 136, 137, 148, 152, 158, 163, 170, 173, 181, 184, 191, 196, 202, 206, 214, 215, 218, 230, 238, 241, 242, 248, 253, 259, 271, 274, 281, 286, 292, 293, 296, 307, 316
Offset: 1
Examples
a(1) = 4 = 2 + 2 = (the smallest prime, 2 = prime(1)) + (digit sum of 2). Similarly, a({2, 3, 5}) = 2*prime({2, 3, 4}), since the digit sum of single-digit primes is the prime itself. a(4) = 13 = 11 + (1 + 1) = A048520(1), the first prime in this sequence. a(6) = 17 = 13 + (1 + 3) = A048520(2), the second prime in this sequence.
Crossrefs
Programs
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PARI
is_A320881(n)=select(p->p+sumdigits(p)==n, primes([n-9*#digits(n), n-2])) \\ Returns the list of all "solutions"; this has the boolean value of true iff the list is nonempty. - M. F. Hasler, Nov 08 2018
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